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Network File System Version 4                                  D. Noveck
Internet-Draft                                         February 27, 2017
Intended status: Informational
Expires: August 31, 2017


         Issues Related to RPC-over-RDMA Internode Round Trips
                draft-dnoveck-nfsv4-rpcrdma-rtissues-03

Abstract

   As currently designed and implemented, the RPC-over-RDMA protocol
   requires use of multiple internode round trips to process some common
   operations.  For example, NFS WRITE operations require use of three
   internode round trips.  This document looks at this issue and
   discusses what can and what should be done to address it, both within
   the context of an extensible version of RPC-over-RDMA and potentially
   outside that framework.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on August 31, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Preliminaries . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Review of the Current Situation . . . . . . . . . . . . . . .   3
     2.1.  Troublesome Requests  . . . . . . . . . . . . . . . . . .   3
     2.2.  WRITE Request Processing Details  . . . . . . . . . . . .   4
     2.3.  READ Request Processing Details . . . . . . . . . . . . .   5
   3.  Near-term Work  . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Target Performance  . . . . . . . . . . . . . . . . . . .   7
     3.2.  Message Continuation  . . . . . . . . . . . . . . . . . .   8
     3.3.  Send-based DDP  . . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Feature Synergy . . . . . . . . . . . . . . . . . . . . .   9
     3.5.  Feature Selection and Negotiation . . . . . . . . . . . .  10
   4.  Possible Future Development . . . . . . . . . . . . . . . . .  12
   5.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Preliminaries

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Introduction

   When many common operations are performed using RPC-over-RDMA,
   additional inter-node round-trip latencies are required to take
   advantage of the performance benefits provided by RDMA Functionality.

   While the latencies involved are generally small, they are a reason
   for concern for two reasons.

   o  With the ongoing improvement of persistent memory technologies,
      such internode latencies, being fixed, can be expected to consume




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      an increasing portion of the total latency required for processing
      NFS requests using RPC-over-RDMA.

   o  High-performance transfers using NFS may be needed outside of a
      machine-room environment.  As RPC-over-RDMA is used in networks of
      campus and metropolitan scale, the internode round-trip time of
      sixteen microseconds per mile becomes an issue.

   Given this background, round trips beyond the minimum necessary need
   to be justified by corresponding benefits.  If they are not, work
   needs to be done to eliminate those excess round trips.

   We are going to look at the existing situation with regard to round-
   trip latency and make some suggestions as to how the issue might be
   best addressed.  We will consider things that could be done in the
   near future and also explore further possibilities that would require
   a longer-term approach to be adopted.

2.  Review of the Current Situation

2.1.  Troublesome Requests

   We will be looking at four sorts of situations:

   o  An RPC operation involving Direct Data Placement of request data
      (e.g., an NFSv3 WRITE or corresponding NFSv4 COMPOUND).

   o  An RPC operation involving Direct Data Placement of response data
      (e.g., an NFSv3 READ or corresponding NFSv4 COMPOUND).

   o  An RPC operation where the request data is longer than the inline
      buffer limit.

   o  An RPC operation where the response data is longer than the inline
      buffer limit.

   These are all simple examples of situations in which explicit RDMA
   operations are used, either to effect Direct Data Placement or to
   respond to message size limits that derive from a limited receive
   buffer size.

   We will survey the resulting latency and overhead issues in an RPC-
   over-RDMA Version One environment in Sections 2.2 and 2.3 below.








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2.2.  WRITE Request Processing Details

   We'll start with the case of a request involving direct placement of
   request data.  In this case, an RDMA READ is used to transfer a DDR-
   eligible data item (e.g. the data to be written) from its location in
   requester memory, to a location selected by the responder.

   Processing proceeds as described below.  Although we are focused on
   internode latency, the time to perform a request also includes such
   things as interrupt latency, overhead involved in interacting with
   the RNIC, and the time for the server to execute the requested
   operation.

   o  First, the memory to be accessed remotely is registered.  This is
      a local operation.

   o  Once the registration has been done, the initial send of the
      request can proceed.  Since this is in the context of connected
      operation, there is an internode round trip involved.  However,
      the next step can proceed after the initial transmission is
      received by the responder.  As a result, only the responder-bound
      side of the transmission contributes to overall operation latency.

   o  The responder, after being notified of the receipt of the request,
      uses RDMA READ to fetch the bulk data.  This involves an internode
      round-trip latency.  After the fetch of the data, the responder
      needs to be notified of the completion of the explicit RDMA
      operation

   o  The responder (after performing the requested operation) sends the
      response.  Again, as this is in the context of connected
      operation, there is an internode round trip involved.  However,
      the next step can proceed after the initial transmission is
      received by the requester.

   o  The memory registered before the request was issued needs to be
      deregistered, before the request is considered complete and the
      sending process restarted.  When remote invalidation is not
      available, the requester, after being notified of the receipt of
      the response, performs a local operation to deregister the memory
      in question.  Alternatively, the responder will use Send With
      Invalidate and the responder's RNIC will effect the deregistration
      before notifying the requester of the response which has been
      received.

   To summarize, if we exclude the actual server execution of the
   request, the latency consists of two internode round-trip latencies
   plus two responder-side interrupt latencies plus one requester-side



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   interrupt latency plus any necessary registration/de-registration
   overhead.  This is in contrast to a request not using explicit RDMA
   operations in which there is a single inter-node round-trip latency
   and one interrupt latency on the requester and the responder.

   The processing of the other sorts of requests mentioned in
   Section 2.1 show both similarities and differences:

   o  Handling of a long request is similar to the above.  The memory
      associated with a position-zero read chunk is registered,
      transferred using RDMA READ, and deregistered.  As a result, we
      have the same overhead and latency issues noted in the case of
      direct data placement, without the corresponding benefits.

   o  The case of direct data placement of response data follows a
      similar pattern.  The important difference is that the transfer of
      the bulk data is performed using RDMA WRITE, rather than RDMA
      READ.  However, because of the way that RDMA WRITE is effected
      over the wire, the latency consequences are different.  See
      Section 2.3 for a detailed discussion.

   o  Handling of a long response is similar to the previous case.

2.3.  READ Request Processing Details

   We'll now discuss the case of a request involving direct placement of
   response data.  In this case, an RDMA WRITE is used to transfer a
   DDR-eligible data item (e.g. the data being read) from its location
   in responder memory, to a location previously selected by the
   requester.

   Processing proceeds as described below.  Although we are focused on
   internode latency, the time to perform a request also includes such
   things as interrupt latency, overhead involved in interacting with
   the RNIC, and the time for the server to execute the requested
   operation.

   o  First, the memory to be accessed remotely is registered.  This is
      a local operation.

   o  Once the registration has been done, the initial send of the
      request can proceed.  Since this is in the context of connected
      operation, there is an internode round trip involved.  However,
      the next step can proceed after the initial transmission is
      received.  As a result, only the responder-bound side of the
      transmission contributes to overall operation latency.





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   o  The responder, after being notified of the receipt of the request,
      proceeds to process the request until the data to be read is
      available in its own memory, with its location determined and
      fixed.  It then uses RDMA WRITE to transfer the bulk data to the
      location in requester memory selected previously.  This involves
      an internode latency, but there is no round trip and thus no
      round-trip latency,

   o  The responder continues processing and sends the inline portion of
      the response.  Again, as this is in the context of connected
      operation, there is an internode round trip involved.  However,
      the next step can proceed immediately.  If the RDMA WRITE or the
      send of the inline portion of the response were to fail, the
      responder can be notified subsequently.

   o  The requester, after being notified of the receipt of the
      response, can analyze it and can access the data written into its
      memory.  Deregistration of the memory originally registered before
      the request was issued can be done using remote invalidation or
      can be done by the requester as a local operation

   To summarize, in this case the additional latency that we saw in
   Section 2.2 does not arise.  Except for the additional overhead due
   to memory registration and invalidation, the situation is the same as
   for a request not using explicit RDMA operations in which there is a
   single inter-node round-trip latency and one interrupt latency on the
   requester and the responder.

3.  Near-term Work

   We are going to consider how the latency and overhead issues
   discussed in Section 2 might be addressed in the context of an
   extensible version of RPC-over-RDMA, such as that proposed in
   [rpcrdmav2].

   In Section 3.1, we will establish a performance target for the
   troublesome requests, based on the performance of requests that do
   not involve long messages or direct data placement.

   We will then consider how extensions might be defined to bring
   latency and overhead for the requests discussed in Section 2.1 into
   line with those for other requests.  There will be two specific
   classes of requests to address:

   o  Those that do not involve direct data placement will be addressed
      in Section 3.2.  In this case, there are no compensating benefits
      justifying the higher overhead and, in some cases, latency.




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   o  The more complicated case of requests that do involve direct data
      placement is discussed in Section 3.3.  In this case, direct data
      placement could serve as a compensating benefit, and the important
      question to be addressed is whether Direct Data Placement can be
      effected without the use of explicit RDMA operations.

   The optional features to deal with each of the classes of messages
   discussed above could be implemented separately.  However, in the
   handling of RPCs with very large amounts of bulk data, the two
   features are synergistic.  This fact makes it desirable to define the
   features as part of the same extension.  See Sections 3.4 and 3.5 for
   details.

3.1.  Target Performance

   As our target, we will look at the latency and overhead associated
   with other sorts of RPC requests, i.e. those that do not use DDP, and
   that have request and response messages which do fit within the
   receive buffer limit.

   Processing proceeds as follows:

   o  The initial send of the request is done.  Since this is in the
      context of connected operation, there is an internode round-trip
      involved.  However, the next step can proceed after the initial
      transmission is received.  As a result, only the responder-bound
      side of the transmission contributes to overall operation latency.

   o  The responder, after being notified of the receipt of the request,
      performs the requested operation and sends the reply.  As in the
      case of the request, there is an internode round trip involved.
      However, the request can be considered complete upon receipt of
      the requester-bound transmission.  The responder-bound
      acknowledgment does not contribute to request latency.

   In this case, there is only a single internode round-trip latency
   necessary to effect the RPC.  Total request latency includes this
   round-trip latency plus interrupt latency on the requester and
   responder, plus the time for the responder to actually perform the
   requested operation.

   Thus the delta between the operations discussed in Section 2 and our
   baseline consists of two portions, one of which applies to all the
   requests we are concerned with and the second of which only applies
   to request which involve use of RDMA READ, as discussed in
   Section 2.2.  The latter category consists of:

   o  One additional internode round-trip latency.



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   o  One additional instance of responder-side interrupt latency.

   The additional overhead necessary to do memory registration and
   deregistration applies to all requests using explicit RDMA
   operations.  The costs will vary with implementation characteristics.
   As a result, in some implementations, it may desirable to replace use
   of RDMA Write with send-based alternatives, while in others, use of
   RDMA Write may be preferable.

3.2.  Message Continuation

   Using multiple RPC-over-RDMA transmissions, in sequence, to send a
   single RPC message avoids the additional latency and overhead
   associated with the use of explicit RDMA operations to transfer
   position-zero read chunks.  In the case of reply chunks, only
   overhead is reduced.

   Although transfer of a single request or reply in N transmissions
   will involve N+1 internode latencies, overall request latency is not
   increased by requiring that operations involving multiple nodes be
   serialized.  Generally, these transmissions are pipelined.

   As an illustration, let's consider the case of a request involving a
   response consisting of two RPC-over-RDMA transmissions.  Even though
   each of these transmissions is acknowledged, that acknowledgement
   does not contribute to request latency.  The second transmission can
   be received by the requester and acted upon without waiting for
   either acknowledgment.

   This situation would require multiple receive-side interrupts but it
   is unlikely to result in extended interrupt latency.  With 1K sends
   (Version One), the second receive will complete about 200 nanoseconds
   after the first assuming a 40Gb/s transmission rate.  Given likely
   interrupt latencies, the first interrupt routine would be able to
   note that the completion of the second receive had already occurred.

3.3.  Send-based DDP

   In order to effect proper placement of request or reply data within
   the context of individual RPC-over-RDMA transmissions, receive
   buffers need to be structured to accommodate this function

   To illustrate the considerations that could lead clients and servers
   to choose particular buffer structures, we will use, as examples, the
   cases of NFS READs and WRITEs of 8K data blocks (or the corresponding
   NFSv4 COMPOUNDs).





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   In such cases, the client and server need to have the DDP-eligible
   bulk data placed in appropriately aligned 8K buffer segments.  Rather
   than being transferred in separate transmissions using explicit RDMA
   operations, a message can be sent so that bulk data is received into
   an appropriate buffer segment.  In this case, it would be excised
   from the XDR payload stream, just as it is in the case of existing
   DDP facilities.

   Consider a server expecting write requests which are usually X bytes
   long or less, exclusive of an 8K bulk data area.  In this case the
   payload stream will most likely be less than X bytes and will fit in
   a buffer segment devoted to that purpose.  The bulk data needs to be
   placed in the subsequent buffer segment in order to align it
   properly, i.e. with the appropriate alignment, in the DDP target
   buffer.  In order to place the data appropriately, the sender (in
   this case, the client) needs to add padding of length X-Y bytes where
   Y is the length of payload stream for the current request.  The case
   of reads is exactly the same except that the sender adding the
   padding is the server.

   To provide send-based DDP as an RPC-over-RDMA extension, the
   framework defined in [rpcrdmav2] could be used.  A new "transport
   characteristic" could be defined which allowed a participant to
   expose the structure of his receive buffers and to identify the
   buffer segments capable of being used as DDP targets.  In addition, a
   new optional message header would have to be defined.  It would be
   defined to provide:

   o  A way to designate a DDP-eligible data item as corresponding to
      target buffer segments, rather than memory registered for RDMA.

   o  A way to indicate to the responder that it should place DDP-
      eligible data items in DDP-targetable buffer segments, rather than
      in memory registered for RDMA.

   o  A way to designate a limited portion of an RPC-over-RDMA
      transmission as constituting the payload stream.

3.4.  Feature Synergy

   While message continuation and send-based DDP each address an
   important class of commonly used messages, their combination allows
   simpler handling of some important classes of messages:

   o  READs and WRITEs transferring larger IOs

   o  COMPOUNDs containing multiple IO operations.




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   o  Operations whose associated payload stream is longer than the
      typical value.

   To accommodate these situations, it would be best to have the
   definition of the headers to support message continuation interact
   with data structures to support send-based DDP as follows:

   o  The header type used for the initial transmission of a message
      continued across multiple transmissions would contain DDP-
      directing structures which support both send-based DDP as well as
      DDP using Explicit RDMA operations.

   o  Buffer references for Send-based DDP should be relative to the
      start of the group of transmissions and should allow transitions
      between buffer segments in different receive buffers.

   o  The header type for messages continuing a group of transmissions
      should not have DDP-related fields but should rely on the initial
      transmission of the group for DDP-related functions.

   o  The portion of each received transmission devoted to the payload
      stream should be part of the header for each message within a
      group of transmissions devoted to a single RPC message.  The
      payload stream for the message as a whole should be the
      concatenation of the streams for each transmission.

   A potential extension supporting these features interacting as
   described above can be found in [rtrext].

3.5.  Feature Selection and Negotiation

   Given that an appropriate extension is likely to support multiple
   OPTIONAL features, special attention will have to be given to
   defining how implementations which might not support the same subset
   of OPTIONAL features can successfully interact.  The goal is to allow
   interacting implementations to get the benefit of features that they
   both support, while allowing implementation pairs that do not share
   support for any of the OPTIONAL features to operate just as base
   Version Two implementations could do in the absence of the potential
   extension.

   It is helpful if each implementation provides characteristics
   defining its level of feature support which the peer implementation
   can test before attempting to use a particular feature.  In other
   similar contexts, the support level concerns the implementation in
   its role as responder, i.e. whether it is prepared to execute a given
   request.  In the case of the potential extension discussed here, most




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   characteristics concern an implementation in its role as receiver.
   One might define characteristics which indicate,

   o  The ability of the implementation, in its role as receiver, to
      process messages continued across multiple RPC-over-RDMA
      transmissions.

   o  The ability of the implementation, in its role as receiver, to
      process messages containing DDP-eligible data items, directly
      placed using a send-based DDP approach.

   Use of such characteristics might allow asymmetric implementations.
   For example, a client might send requests containing DDP-eligible
   data items using send-based DDP without being able to accept messages
   containing data items using send-based DDP.  That is a likely
   implementation pattern, given the greater performance benefits of
   avoiding use of RDMA Read.

   Further useful characteristics would apply to the implementation in
   its role of responder.  For instance,

   o  The ability of the implementation, in its role as responder, to
      accept and process requests which REQUIRE that DDP-eligible data
      items in the response be sent using send-based DDP.  The presence
      of this characteristic would allow a requester to avoid
      registering memory to be used to accommodate DDP-eligible data
      items in the response.

   o  The ability of the implementation, in its role as responder, to
      send responses using message continuation, as opposed to using a
      reply chunk.

   Because of the potentially different needs of operations in the
   forward and backward directions, it may be desirable to separate the
   receiver-based characteristics according the direction of operation
   that they apply to.

   A further issue relates to the role of explicit RDMA operations in
   connection with backwards operation.  Although, no current protocols
   require support for DDP or transfer of large messages when operating
   in the backward direction, the protocol is designed to allow such
   support to be developed in the future.  Since the protocol, with the
   extension discussed here is likely to have multiple methods of
   providing these functions, we have a number of possible choices
   regarding the role of chunk-based methods of providing these
   functions





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   o  Support for chunk-based operation remains a REQUIREMENT for
      responders, and requesters always have the option of using it,
      regardless of the direction of operation.

      Requesters could select alternatives to the use of explicit RDMA
      operations when these are supported by the responder

   o  When operating in the forward direction, support for chunk-based
      operation remains a REQUIREMENT for responders (i.e. servers), and
      requesters (i.e. clients).

      When operating in the backward direction, support for chunk-based
      is OPTIONAL for responders (i.e. clients) allowing requesters
      (i.e. servers) to select use of explicit RDMA operations or
      alternatives when each of these is supported by the requester.

   o  Support for chunk-based operation is treated as OPTIONAL for
      responders, regardless of the direction of operation.

      In this case, requesters would select use of explicit RDMA
      operations or alternatives when each of these is supported by the
      responder.  For a considerable time, support for explicit RDMA
      operations would be a practical necessity, even if not a
      REQUIREMENT, for operation in the forward direction.

4.  Possible Future Development

   Although the reduction of explicit RDMA operation reduces the number
   of inter-node round trips and eliminates sequences of operations in
   which multiple round-trip latencies are serialized with server
   interrupt latencies, the use of connected operations means that
   round-trip latencies will always be present, since each message is
   acknowledged.

   One avenue that has been considered is use of unreliable-datagram
   (UD) transmission in environments where the "unreliable" transmission
   is sufficiently reliable that RPC replay can deal with a very low
   rate of message loss.  For example, UD in Infiniband specifies a low
   enough rate of frame loss to make this a viable approach,
   particularly for use in supporting protocols such as NFSv4.1, that
   contain their own facilities to ensure exactly-once semantics.

   With this sort of arrangement, request latency is still the same.
   However, since the acknowledgements are not serving any substantial
   function, it is tempting to consider removing them, as they do take
   up some transmission bandwidth, that might be used otherwise, if the
   protocol were to reach the goal of effectively using the underlying
   medium.



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   The size of such wasted transmission bandwidth depends on the average
   message size and many implementation considerations regarding how
   acknowledgments are done.  In any case, given expected message sizes,
   the wasted transmission bandwidth will be very small.

   When RPC messages are quite small, acknowledgments may be of concern.
   However, in that situation, a better response would be transfer
   multiple RPC messages within a single RPC-over-RDMA transmission.

   When multiple RPC messages are combined into a single transmission,
   the overhead of interfacing with the RNIC, particularly the interrupt
   handling overhead, is amortized over multiple RPC messages.

   Although this technique is quite outside the spirit of existing RPC-
   over-RDMA implementations, it appears possible to define new header
   types capable of supporting this sort of transmission, using the
   extension framework described in [rpcrdmav2].

5.  Summary

   We've examined the issue of round-trip latency and concluded:

   o  That the number of round trips per se is not as important as the
      contribution of any extra round trips to overall request latency.

   o  That the latency issue can be addressed using the extension
      mechanism provided for in [rpcrdmav2].

   o  That in many cases in which latency is not an issue, there may be
      overhead issues that can be addressed using the same sorts of
      techniques as those useful in latency reduction, again using the
      extension mechanism provided for in [rpcrdmav2].

   As it seems that the features sketched out could put internode
   latencies and overhead for a large class of requests back to the
   baseline value for the RPC paradigm, more detailed definition of the
   required extension functionality is in order.

   We've also looked at round trips at the physical level, in that
   acknowledgments are sent in circumstances where there is no obvious
   need for them.  With regard to these, we have concluded:

   o  That these acknowledgements do not contribute to request latency.

   o  That while UD transmission can remove acknowledgements of limited
      value, the performance benefits are not sufficient to justify the
      disruption that this would entail.




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   o  That issues with transmission bandwidth overhead in a small-
      message environment are better addressed by combining multiple RPC
      messages in a single RPC-over-RDMA transmission.  This is
      particularly so, because such a step is likely to reduce overhead
      in such environments as well

   As the features described involve the use of alternatives to explicit
   RDMA operations, in performing direct data placement and in
   transferring messages that are larger than the receive buffer limit,
   it is appropriate to understand the role that such operations are
   expected to have once the extensions discussed in this document are
   fully specified and implemented.

   It is important to note that these extensions are OPTIONAL and are
   expected to remain so, while support for explicit RDMA operations
   will remain an integral part of RPC-over-RDMA.

   Given this framework, the degree to which explicit RDMA operations
   will be used will reflect future implementation choices and needs.
   While we have been focusing on cases in which other options might be
   more efficient in some cases, it worth looking also at the cases in
   which explicit RDMA operations are likely to remain preferable:

   o  In some environments in which direct data placement to memory of a
      certain alignment does not meet application requirements and in
      which data needs to be read into a particular address on the
      client.  Also, large physically contiguous buffers may be required
      in some environments.  In these situations, send-based DDP is not
      an option.

   o  Where large transfers are to be done, there will be limits to the
      capacity of send-based DDP to provide the required functionality,
      since the basic pattern using send/receive is to allocate a pool
      of memory to contain receive buffers in advance of issuing
      requests.  While this issue can be mitigated by use of message
      continuation, tying up large numbers of credits for a single
      request can cause difficult issues as well.  As a result, send-
      based DDP may be restricted to IO's of limited size, although the
      specific limits will depend on the details of the specific
      implementation.

6.  Security Considerations

   This document does not raise any security issues.







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7.  IANA Considerations

   This document does not require any actions by IANA.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [rfc5666bis]
              Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call",
              February 2017, <http://www.ietf.org/id/
              draft-ietf-nfsv4-rfc5666bis-10.txt>.

              Work in progress.

8.2.  Informative References

   [RFC5666]  Talpey, T. and B. Callaghan, "Remote Direct Memory Access
              Transport for Remote Procedure Call", RFC 5666,
              DOI 10.17487/RFC5666, January 2010,
              <http://www.rfc-editor.org/info/rfc5666>.

   [rfc5667bis]
              Lever, C., Ed., "Network File System (NFS) Upper Layer
              Binding To RPC-Over-RDMA", February 2017,
              <http://www.ietf.org/id/
              draft-ietf-nfsv4-rfc5667bision-06.txt>.

              Work in progress.

   [rpcrdmav2]
              Lever, C., Ed. and D. Noveck, "RPC-over-RDMA Version Two",
              December 2016, <http://www.ietf.org/id/
              draft-cel-nfsv4-rpcrdma-version-two-03.txt>.

              Work in progress.

   [rtrext]   Noveck, D., "RPC-over-RDMA Extensions to Reduce Internode
              Round-trips", December 2016, <http://www.ietf.org/id/
              draft-dnoveck-nfsv4-rpcrdma-rtrext-01.txt>.

              Work in progress.



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Appendix A.  Acknowledgements

   The author gratefully acknowledges the work of Brent Callaghan and
   Tom Talpey producing the original RPC-over-RDMA Version One
   specification [RFC5666] and also Tom's work in helping to clarify
   that specification.

   The author also wishes to thank Chuck Lever for his work reviving
   RDMA support for NFS in [rfc5666bis], [rfc5667bis], and [rpcrdmav2],
   and for helpful discussion regarding RPC-over-RDMA latency issues.

Author's Address

   David Noveck
   26 Locust Avenue
   Lexington, MA  02421
   USA

   Phone: +1 781-572-8038
   Email: davenoveck@gmail.com































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