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:
发自我的 iPhone
在 2016年3月27日，下午11:20，Peter Zijlstra <pet...@infradead.org>
写道：
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.
