Re: [LKP] [mm] 42a3003535: will-it-scale.per_process_ops -25.9% regression

Johannes Weiner
2019-05-21T15:14:00Z

On Tue, May 21, 2019 at 09:46:46PM +0800, kernel test robot wrote:
> On Mon, May 20, 2019 at 05:53:28PM -0400, Johannes Weiner wrote:
> > Hello,
> >
> > On Mon, May 20, 2019 at 02:35:34PM +0800, kernel test robot wrote:
> > > Greeting,
> > >
> > > FYI, we noticed a -25.9% regression of will-it-scale.per_process_ops due to commit:
> > >
> > >
> > > commit: 42a300353577ccc17ecc627b8570a89fa1678bec ("mm: memcontrol: fix recursive statistics correctness & scalabilty")
> > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> > >
> > > in testcase: will-it-scale
> > > on test machine: 192 threads Skylake-SP with 256G memory
> > > with following parameters:
> >
> > Ouch. That has to be the additional cache footprint of the split
> > local/recursive stat counters, rather than the extra instructions.
> >
> > Could you please try re-running the test on that host with the below
> > patch applied?
>
> Hi,
>
> The patch can fix the regression.
>
> tests: 1
> testcase/path_params/tbox_group/run: will-it-scale/performance-process-100%-page_fault3/lkp-skl-4sp1
>
> db9adbcbe7 ("mm: memcontrol: move stat/event counting functions out-of-line")
> 8d8245997d ("mm: memcontrol: don't batch updates of local VM stats and events")
>
> db9adbcbe740e098 8d8245997dbd17c5056094f15c
> ---------------- --------------------------
> %stddev change %stddev
> \ | \
> 87819982 85307742 will-it-scale.workload
> 457395 444310 will-it-scale.per_process_ops

Fantastic, thank you for verifying! I'm going to take that as a
Tested-by.