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Subject: Re: still seeing single client NFS4ERR_DELAY / CB_RECALL
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20200817222034.GA6390@fieldses.org>
Date:   Tue, 18 Aug 2020 11:27:03 -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 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:
>> Hi Bruce-
>>=20
>>> On Aug 11, 2020, at 9:31 AM, Chuck Lever <chuck.lever@oracle.com> =
wrote:
>>>=20
>>>> On Aug 10, 2020, at 4:10 PM, Bruce Fields <bfields@fieldses.org> =
wrote:
>>>>=20
>>>> 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.
>>>>>=20
>>>>> 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.
>>>>=20
>>>> Oh, OK, I was assuming this was a regression.
>>>=20
>>> 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.
>>=20
>> 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.
>=20
> Well, that's interesting.
>=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

Quick follow-up:

I reverted a couple of hunks that appear to be for the next commit,
and fd4f83fd7dfb builds now. Tested, and this is the bad commit (where
the performance regression starts).


>> 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
> --b.

--
Chuck Lever