linux-kernel - Re: 5.4.188 and later: massive performance regression with nfsd

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Date:   Fri, 20 May 2022 15:36:43 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     Wolfgang Walter <linux@...m.de>,
        linux-stable <stable@...r.kernel.org>,
        Trond Myklebust <trondmy@...il.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: 5.4.188 and later: massive performance regression with nfsd



> On May 11, 2022, at 10:36 AM, Chuck Lever III <chuck.lever@...cle.com> wrote:
> 
> 
> 
>> On May 11, 2022, at 10:23 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
>> 
>> On Wed, May 11, 2022 at 02:16:19PM +0000, Chuck Lever III wrote:
>>> 
>>> 
>>>> On May 11, 2022, at 8:38 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
>>>> 
>>>> On Wed, May 11, 2022 at 12:03:13PM +0200, Wolfgang Walter wrote:
>>>>> Hi,
>>>>> 
>>>>> starting with 5.4.188 wie see a massive performance regression on our
>>>>> nfs-server. It basically is serving requests very very slowly with cpu
>>>>> utilization of 100% (with 5.4.187 and earlier it is 10%) so that it is
>>>>> unusable as a fileserver.
>>>>> 
>>>>> The culprit are commits (or one of it):
>>>>> 
>>>>> c32f1041382a88b17da5736886da4a492353a1bb "nfsd: cleanup
>>>>> nfsd_file_lru_dispose()"
>>>>> 628adfa21815f74c04724abc85847f24b5dd1645 "nfsd: Containerise filecache
>>>>> laundrette"
>>>>> 
>>>>> (upstream 36ebbdb96b694dd9c6b25ad98f2bbd263d022b63 and
>>>>> 9542e6a643fc69d528dfb3303f145719c61d3050)
>>>>> 
>>>>> If I revert them in v5.4.192 the kernel works as before and performance is
>>>>> ok again.
>>>>> 
>>>>> I did not try to revert them one by one as any disruption of our nfs-server
>>>>> is a severe problem for us and I'm not sure if they are related.
>>>>> 
>>>>> 5.10 and 5.15 both always performed very badly on our nfs-server in a
>>>>> similar way so we were stuck with 5.4.
>>>>> 
>>>>> I now think this is because of 36ebbdb96b694dd9c6b25ad98f2bbd263d022b63
>>>>> and/or 9542e6a643fc69d528dfb3303f145719c61d3050 though I didn't tried to
>>>>> revert them in 5.15 yet.
>>>> 
>>>> Odds are 5.18-rc6 is also a problem?
>>> 
>>> We believe that
>>> 
>>> 6b8a94332ee4 ("nfsd: Fix a write performance regression")
>>> 
>>> addresses the performance regression. It was merged into 5.18-rc.
>> 
>> And into 5.17.4 if someone wants to try that release.
> 
> I don't have a lot of time to backport this one myself, so
> I welcome anyone who wants to apply that commit to their
> favorite LTS kernel and test it for us.
> 
> 
>>>> If so, I'll just wait for the fix to get into Linus's tree as this does
>>>> not seem to be a stable-tree-only issue.
>>> 
>>> Unfortunately I've received a recent report that the fix introduces
>>> a "sleep while spinlock is held" for NFSv4.0 in rare cases.
>> 
>> Ick, not good, any potential fixes for that?
> 
> Not yet. I was at LSF last week, so I've just started digging
> into this one. I've confirmed that the report is a real bug,
> but we still don't know how hard it is to hit it with real
> workloads.

We believe the following, which should be part of the first
NFSD pull request for 5.19, will properly address the splat.

https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/commit/?h=for-next&id=556082f5e5d7ecfd0ee45c3641e2b364bff9ee44


--
Chuck Lever