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Date:   Wed, 19 Aug 2020 17:29:27 -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: <20200819212927.GB30476@fieldses.org>
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On Tue, Aug 18, 2020 at 05:26:26PM -0400, Chuck Lever wrote:
> 
> > On Aug 17, 2020, at 6:20 PM, Bruce Fields <bfields@fieldses.org> wrote:
> > 
> > On Sun, Aug 16, 2020 at 04:46:00PM -0400, Chuck Lever wrote:
> > 
> >> 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.
> 
> nfsd_file_acquire() always calls fh_verify() before it invokes nfsd_open().
> Replacing nfs4_get_vfs_file's nfsd_open() call with nfsd_file_acquire() adds
> almost 10 million fh_verify() calls to my test run.

Checking out the code as of fd4f83fd7dfb....

nfsd_file_acquire() calls nfsd_open_verified().

And nfsd_open() is basically just fh_verify()+nfsd_open_verified().

So it doesn't look like the replacement of nfsd_open() by
nfsd_file_acquire() should have changed the number of fh_verify() calls.

--b.

> 
> On my server, fh_verify() is quite expensive. Most of the cost is in the
> prepare_creds() call.
> 
> --
> Chuck Lever
> 
>