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

[Wangnan (F)]

On 2016/3/28 9:58, Wangnan (F) wrote:
> On 2016/3/28 9:07, Wangnan (F) wrote:
> > 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.
>
> Find the reason of these outliners.
>
> If perf and 'test-ring-buffer' are scheduled on different processors,
> the performance is bad. I think cache is the main reason.
>
> I will redo the test, bind them to cores on same CPU.
>
> Thank you.

Test method improvements:

1. Set CPU freq:

 # for f in /sys/devices/system/cpu/cpufreq/policy*/scaling_governor  ; 
do echo performance > $f ; done

2. Bind core:
Add following code into head of test-ring-buffer:

        CPU_ZERO(&mask);
        CPU_SET(6, &mask);
        pthread_setaffinity_np(pthread_self(), sizeof(mask), &mask);
        pthread_yield();

3. Bind core (perf):

Use following command to start perf:

 # taskset -c 7 ./perf record -o /dev/null --no-buildid-cache -e 
raw_syscalls:* test-ring-buffer

New result of 100 test data in both cases:

                  MEAN         STDVAR
BASE            800214.950    2853.083
RAWPERF.PRE    2253846.700    9997.014
RAWPERF.POST   2257495.540    8516.293

Thank you.