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Subject: Re: still seeing single client NFS4ERR_DELAY / CB_RECALL
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20200819212927.GB30476@fieldses.org>
Date:   Thu, 20 Aug 2020 08:56:06 -0400
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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To:     Bruce Fields <bfields@fieldses.org>
Sender: linux-nfs-owner@vger.kernel.org
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> On Aug 19, 2020, at 5:29 PM, Bruce Fields <bfields@fieldses.org> =
wrote:
>=20
> On Tue, Aug 18, 2020 at 05:26:26PM -0400, Chuck Lever wrote:
>>=20
>>> On Aug 17, 2020, at 6:20 PM, Bruce Fields <bfields@fieldses.org> =
wrote:
>>>=20
>>> On Sun, Aug 16, 2020 at 04:46:00PM -0400, Chuck Lever wrote:
>>>=20
>>>> In order of application:
>>>>=20
>>>> 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.
>>>>=20
>>>> fd4f83fd7dfb ("nfsd: convert nfs4_file->fi_fds array to use =
nfsd_files")
>>>> Does not build
>>>>=20
>>>> 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
>>>>=20
>>>> Can you take a look and see if there's anything obvious?
>>>=20
>>> Unfortunately nothing about the file cache code is very obvious to =
me.
>>> I'm looking at it....
>>>=20
>>> 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.
>>>=20
>>> Or maybe it's the lease break there.
>>=20
>> 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.
>=20
> Checking out the code as of fd4f83fd7dfb....
>=20
> nfsd_file_acquire() calls nfsd_open_verified().
>=20
> And nfsd_open() is basically just fh_verify()+nfsd_open_verified().
>=20
> So it doesn't look like the replacement of nfsd_open() by
> nfsd_file_acquire() should have changed the number of fh_verify() =
calls.

Agreed, the increase is a little mysterious.


> --b.
>=20
>>=20
>> On my server, fh_verify() is quite expensive. Most of the cost is in =
the
>> prepare_creds() call.

--
Chuck Lever