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Date:   Mon, 17 Aug 2020 18:20:34 -0400
From:   Bruce Fields <bfields@fieldses.org>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: still seeing single client NFS4ERR_DELAY / CB_RECALL
Message-ID: <20200817222034.GA6390@fieldses.org>
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On Sun, Aug 16, 2020 at 04:46:00PM -0400, Chuck Lever wrote:
> Hi Bruce-
> 
> > On Aug 11, 2020, at 9:31 AM, Chuck Lever <chuck.lever@oracle.com> wrote:
> > 
> >> On Aug 10, 2020, at 4:10 PM, Bruce Fields <bfields@fieldses.org> wrote:
> >> 
> >> On Mon, Aug 10, 2020 at 04:01:00PM -0400, Chuck Lever wrote:
> >>> Roughly the same result with this patch as with the first one. The
> >>> first one is a little better. Plus, I think the Solaris NFS server
> >>> hands out write delegations on v4.0, and I haven't heard of a
> >>> significant issue there. It's heuristics may be different, though.
> >>> 
> >>> So, it might be that NFSv4.0 has always run significantly slower. I
> >>> will have to try a v5.4 or older server to see.
> >> 
> >> Oh, OK, I was assuming this was a regression.
> > 
> > Me too. Looks like it is: NFSv4.0 always runs slower, but I see
> > it get significantly worse between v5.4 and 5.5. I will post more
> > quantified results soon.
> 
> It took me a while to get plausible bisection results. The problem
> appears in the midst of the NFSD filecache patches merged in v5.4.

Well, that's interesting.

> In order of application:
> 
> 5920afa3c85f ("nfsd: hook nfsd_commit up to the nfsd_file cache")
> 961.68user 5252.40system 20:12.30elapsed 512%CPU, 2541 DELAY errors
> These results are similar to v5.3.
> 
> fd4f83fd7dfb ("nfsd: convert nfs4_file->fi_fds array to use nfsd_files")
> Does not build
> 
> eb82dd393744 ("nfsd: convert fi_deleg_file and ls_file fields to nfsd_file")
> 966.92user 5425.47system 33:52.79elapsed 314%CPU, 1330 DELAY errors
> 
> Can you take a look and see if there's anything obvious?

Unfortunately nothing about the file cache code is very obvious to me.
I'm looking at it....

It adds some new nfserr_jukebox returns in nfsd_file_acquire.  Those
mostly look like kmalloc failures, the one I'm not sure about is the
NFSD_FILE_HASHED check.

Or maybe it's the lease break there.

--b.