On Tue, 19 Nov 2024 at 17:31, Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote: > > > > > On Nov 19, 2024, at 10:09 AM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > > > > On Tue, 2024-11-19 at 06:45 -0500, Jeff Layton wrote: > >> We attempted to implement the "delstid" draft for v6.13, but have had > >> to drop the patches for it. After merge, we got a couple of reports > >> of > >> a performance issue due to the OPEN_XOR_DELEGATION patch: > >> > >> > >> https://lore.kernel.org/linux-nfs/202409161645.d44bced5-oliver.sang@xxxxxxxxx/ > >> > >> Once we enable OPEN_XOR_DELEGATION support, the fsmark "App Overhead" > >> statistic spikes significantly. The kernel patch for this is very > >> simple, and doesn't seem likely to cause a performance issue on its > >> own. My theory is that this test is one that causes the client to > >> return the delegation, and since it doesn't have an open stateid, it > >> has to reestablish one during the test run, and that causes the app > >> overhead stat to spike. > >> > >> Trond, Tom, Mike -- I know that the HS Anvil has support for > >> OPEN_XOR_DELEGATION. If you run the fsmark test against it with that > >> support both enabled and disabled (either on the client or server > >> side), do you see a similar spike in "App Overhead"? > >> > >> If so, then I suspect we need to consider limiting the use of that > >> flag > >> in some cases. I have no idea what heuristic we'd use to decide this > >> though. > > > > As already stated when we discussed this at Bakeathon: the server is > > still in charge of heuristics w.r.t. whether or not there may be > > contention for the file. The OPEN_XOR_DELEGATION flag changes nothing > > in that respect. > > fsmark is a single-client test. There should be no contention > for any files during this test. > > > > Yes, I'm sure you can find tests which cause recalls of delegations, > > and those will be marginally slower when the client has to re-establish > > an open stateid. > > The fsmark result regressed 92%. > > > > However the issue with those tests is that they are > > deliberately setting up a situation where the server ideally shouldn't > > be handing out a delegation at all. > > > > Furthermore, this is no different than a situation where the client > > used a delegation to cache the open (i.e. avoid sending an OPEN call) > > after the application closed the file and then later re-opened it. > > So the point is that this is not a situation that is unique to > > OPEN_XOR_DELEGATION. It is just a consequence of the client's ability > > to cache open state. > > The regression was bisected to Jeff's XOR patch on two > separate occasions. This does indeed appear to be a > situation that is unique to OPEN_XOR_DELEGATION. > > It's possible that our theory of the failure is wrong. > As developers of the only other server implementation of > OPEN_XOR_DELEGATION, can Hammerspace help us troubleshoot > this issue? > Doesn't Tigran's dcache.org nfs4j server also support OPEN_XOR_DELEGATION? Ced -- Cedric Blancher <cedric.blancher@xxxxxxxxx> [https://plus.google.com/u/0/+CedricBlancher/] Institute Pasteur
