Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end

[Wangnan (F)]

On 2016/3/27 23:30, pi3orama wrote:
> åèæç iPhone
>
> > å 2016å3æ27æïäå11:20ïPeter Zijlstra <peterz@xxxxxxxxxxxxx> åéï
> >
> > On Fri, Mar 25, 2016 at 10:14:36PM +0800, Wangnan (F) wrote:
> > > > > I think you enabled some unusual config options?
> > x86_64-defconfig
> >
> > > > You must enabled CONFIG_OPTIMIZE_INLINING. Now I get similar result:
> > It has that indeed.
> >
> > > After enabling CONFIG_OPTIMIZE_INLINING:
> > >
> > > Test its performance by calling 'close(-1)' for 3000000 times and
> > > use 'perf record -o /dev/null -e raw_syscalls:* test-ring-buffer' to
> > > capture system calls:
> > >
> > >                   MEAN         STDVAR
> > > BASE            800077.1     23448.13
> > > RAWPERF.PRE    2465858.0    603473.70
> > > RAWPERF.POST   2471925.0    609437.60
> > >
> > > Considering the high stdvar, after applying this patch the performance
> > > is not change.
> > Why is your variance so immense? And doesn't that render the
> > measurements pointless?
> For some unknown reason, about
> 10% of these results raises 2 times of normal
> results. Say, "normal results" are about
> 2200000, but those "outliers" are about
> 4400000 (I can't access raw data now).
> Variance becomes much smaller if I remove
> those outliers.

After manually removing outliners (remove 10 outliners from 100 raw
data points in each data set):


                 MEAN         STDVAR
BASE            800077.1     23448.13
RAWPERF.PRE    2265741.0     10421.35
RAWPERF.POST   2269826.0     10507.45

Thank you.

> I guess the outliers is caused by some type
> of lock stepping? No clue about it.
>
> Thank you.