Re: 5.4.188 and later: massive performance regression with nfsd

[Greg KH <gregkh@linuxfoundation.org>]

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@linuxfoundation.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.

> > 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?

thanks,

greg k-h