On Wed, Oct 18, 2023 at 03:07:20PM +0800, Oliver Sang wrote:
> hi, Greg Kroah-Hartman,
>
> On Tue, Oct 17, 2023 at 06:56:56PM +0200, Greg Kroah-Hartman wrote:
> > On Tue, Oct 17, 2023 at 11:06:42PM +0800, kernel test robot wrote:
> > >
> > >
> > > Hello,
> > >
> > > kernel test robot noticed a -99.8% regression of stress-ng.splice.ops_per_sec on:
> > >
> > >
> > > commit: 1b057bd800c3ea0c926191d7950cd2365eddc9bb ("drivers/char/mem: implement splice() for /dev/zero, /dev/full")
> > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> > >
> > > testcase: stress-ng
> > > test machine: 64 threads 2 sockets Intel(R) Xeon(R) Gold 6346 CPU @ 3.10GHz (Ice Lake) with 256G memory
> > > parameters:
> > >
> > > nr_threads: 100%
> > > testtime: 60s
> > > class: pipe
> > > test: splice
> > > cpufreq_governor: performance
> > >
> > >
> > > In addition to that, the commit also has significant impact on the following tests:
> > >
> > > +------------------+-------------------------------------------------------------------------------------------------+
> > > | testcase: change | stress-ng: stress-ng.splice.ops_per_sec 38.9% improvement |
> >
> > So everything now goes faster, right? -99.8% regression means 99.8%
> > faster?
>
> let me clarify.
>
> our auto bisect captured this commit as 'first bad commit' in two tests.
>
> Test 1:
>
> it found a (very big) regression comparing to parent commit.
>
> 19e3e6cdfdc73400 1b057bd800c3ea0c926191d7950
> ---------------- ---------------------------
> %stddev %change %stddev
> \ | \
> 12433266 -99.8% 22893 ± 3% stress-ng.splice.ops_per_sec
>
> the detail data for parent in multi-runs:
> "stress-ng.splice.ops_per_sec": [
stress-ng is a performance test?
> 12444442.19,
> 12599010.87,
> 12416009.38,
> 12494132.89,
> 12286766.76,
> 12359235.82
> ],
>
> for 1b057bd800:
> "stress-ng.splice.ops_per_sec": [
> 24055.57,
> 23235.46,
> 22142.13,
> 23782.13,
> 21732.13,
> 22415.46
> ],
>
> so this is much slower.
That's odd given that as was pointed out, this test does not even touch
the code paths that this patch changed.
confused,
greg k-h
