On Thu, 2020-06-11 at 10:06 +0800, kernel test robot wrote:
> On Sun, Jun 07, 2020 at 09:13:08AM +0800, Ian Kent wrote:
> > On Sat, 2020-06-06 at 20:18 +0200, Greg Kroah-Hartman wrote:
> > > On Sat, Jun 06, 2020 at 11:52:16PM +0800, kernel test robot
> > > wrote:
> > > > Greeting,
> > > >
> > > > FYI, we noticed a 11827.2% improvement of stress-
> > > > ng.stream.ops_per_sec due to commit:
> > > >
> > > >
> > > > commit: ea7c5fc39ab005b501e0c7666c29db36321e4f74 ("[PATCH 1/4]
> > > > kernfs: switch kernfs to use an rwsem")
> > > > url:
> > > > https://github.com/0day-ci/linux/commits/Ian-Kent/kernfs-proposed-locking-and-concurrency-improvement/20200525-134849
> > > >
> > >
> > > Seriously? That's a huge performance increase, and one that
> > > feels
> > > really odd. Why would a stress-ng test be touching sysfs?
> >
> > That is unusually high even if there's a lot of sysfs or kernfs
> > activity and that patch shouldn't improve VFS path walk contention
> > very much even if it is present.
> >
> > Maybe I've missed something, and the information provided doesn't
> > seem to be quite enough to even make a start on it.
> >
> > That's going to need some analysis which, for my part, will need to
> > wait probably until around rc1 time frame to allow me to get
> > through
> > the push down stack (reactive, postponed due to other priorities)
> > of
> > jobs I have in order to get back to the fifo queue (longer term
> > tasks,
> > of which this is one) list of jobs I need to do as well, ;)
> >
> > Please, kernel test robot, more information about this test and
> > what
> > it's doing.
> >
>
> Hi Ian,
>
> We increased the timeout of stress-ng from 1s to 32s, and there's
> only
> 3% improvement of stress-ng.stream.ops_per_sec:
>
> fefcfc968723caf9 ea7c5fc39ab005b501e0c7666c testcase/testparams/tes
> tbox
> ---------------- -------------------------- -----------------------
> ----
> %stddev change %stddev
> \ | \
> 10686 3% 11037 stress-ng/cpu-cache-
> performance-1HDD-100%-32s-ucode=0x500002c/lkp-csl-2sp5
> 10686 3% 11037 GEO-MEAN stress-
> ng.stream.ops_per_sec
>
> It seems the result of stress-ng is inaccurate if test time too
> short, we'll increase the test time to avoid unreasonable results,
> sorry for the inconvenience.
Haha, I was worried there wasn't anything that could be done to
work out what was wrong.
I had tried to reproduce it, and failed since the job file specifies
a host config that I simply don't have, and I don't get how to alter
the job to suit, or how to specify a host definition file.
I also couldn't work out what parameters where used in running the
test so I was about to ask on the lkp list after working through
this in a VM.
So your timing on looking into this is fortunate, for sure.
Thank you very much for that.
Now, Greg, there's that locking I changed around kernfs_refresh_inode()
that I need to fix which I re-considered as a result of this, so that's
a plus for the testing because it's certainly wrong.
I'll have another look at that and boot test it on a couple of systems
then post a v2 for you to consider. What I've done might offend your
sensibilities as it does mine, or perhaps not so much.
Ian
