Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rpcrdma-bidirection-05
Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com> Thu, 12 January 2017 18:35 UTC
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From: Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>
Date: Thu, 12 Jan 2017 12:35:26 -0600
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To: Spencer Shepler <spencer.shepler@gmail.com>
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Cc: draft-ietf-nfsv4-rpcrdma-bidirection@ietf.org, NFSv4 <nfsv4@ietf.org>
Subject: Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rpcrdma-bidirection-05
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Hi, Spencer (S), On Jan 12, 2017 12:32, "spencer shepler" <spencer.shepler@gmail.com> wrote: Yes, Spencer D. I believe we are ready with the updates that Chuck has in-hand. Thanks for the review. Spencer S Excellent. I'll request Last Call when Chuck submits his update. Spencer On Tue, Jan 10, 2017 at 7:26 PM, Spencer Dawkins at IETF < spencerdawkins.ietf@gmail.com> wrote: > Hi, Chuck, > > On Tue, Jan 10, 2017 at 5:02 PM, Chuck Lever <chuck.lever@oracle.com> > wrote: > >> >> > On Jan 10, 2017, at 5:13 PM, Spencer Dawkins at IETF < >> spencerdawkins.ietf@gmail.com> wrote: >> > >> > Hi, Chuck, >> > >> > On Tue, Jan 10, 2017 at 3:47 PM, Chuck Lever <chuck.lever@oracle.com> >> wrote: >> > Again, thanks for your review! Responses below. >> > >> > Oh, thank YOU. You responded while I still have this draft in my solid >> state memory :-) ... >> > >> > It looks like we're good except for the last point. >> > >> > > On Jan 10, 2017, at 4:32 PM, Spencer Dawkins at IETF < >> spencerdawkins.ietf@gmail.com> wrote: >> >> [ snipped ] >> >> > > In this text, >> > > >> > > When message direction is not fully determined by context (e.g., >> > > suggested by the definition of the RPC-over-RDMA version that is in >> > > use) or by an accompanying RPC message payload with a call >> direction >> > > field, it is not possible for the receiver to tell with certainty >> > > whether the header credit value is a request or grant. In such >> > > cases, the receiver MUST NOT use the header's credit value. >> > > >> > > does RDMA work at all, if the credit value can't be used? >> > >> > What this means is the receiver MUST NOT update its credit accounting >> > based on the information in this header. These foggy situations should >> > be exceptionally rare. >> > >> > "MUST ignore" might be more appropriate. >> > >> > I think what I was thinking about, is whether this situation can lead >> to deadlock. >> >> The credit grant value has to be ignored whenever the forward and backward >> grants are not the same value (which is typical in current >> implementations). >> >> With the current set of protocols, the only case like this is RDMA_ERROR, >> which is almost never used. Ignoring the credit value for those messages >> doesn't seem problematic. >> >> If the backward credit grant (which is likely to be smaller) is suddenly >> used in the forward direction, for that one message, the forward requester >> would wait for any outstanding replies before sending more requests. The >> next message from the responder would restore the forward credit grant to >> its correct value. >> >> I don't think a deadlock could occur unless the grant value went to zero, >> and that is already forbidden by rfc5666bis. > > > I had forgotten that detail. Thanks for the wake-up call! > > >> Another way to address this I suppose would be to ensure the grant values >> in both directions are always the same. >> >> >> > I guess I should back up and ask a more basic question, which is >> whether you'd be able to recognize that this situation applies from looking >> at the definition of the RPC-over-RDMA version, so you could just say "I'm >> not going to do bidirectional" when a transport connection is established, >> rather than trying to figure out that there's a problem during request >> processing. >> >> An implementer would be able to tell where these corner cases are, since >> her implementation has to ignore the credit value in those cases. But >> maybe I'm missing something. >> > > I'm thinking the guy who's missing something is me ;-) > > I think we're good to go on this document. > > Spencer (S), would you agree? > > Spencer (D) > > > _______________________________________________ > nfsv4 mailing list > nfsv4@ietf.org > https://www.ietf.org/mailman/listinfo/nfsv4 > >
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Tom Talpey
- [nfsv4] AD Evaluation for draft-ietf-nfsv4-rpcrdm… Spencer Dawkins at IETF
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Chuck Lever
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Spencer Dawkins at IETF
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Chuck Lever
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Chuck Lever
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Spencer Dawkins at IETF
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… spencer shepler
- Re: [nfsv4] AD Evaluation for draft-ietf-nfsv4-rp… Spencer Dawkins at IETF