Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

From: Ingo Molnar <[email-masked]>
Date: Mon, 28 Oct 2013 17:24:38 +0100

* Neil Horman <[email-masked]> wrote:

> Looking at the specific cpu counters we get this:
> 
> Base:
>      Total time: 0.179 [sec]
> 
>  Performance counter stats for 'perf bench sched messaging -- bash -c echo 1 > /sys/module/csum_test/parameters/test_fire' (20 runs):
> 
>        1571.304618 task-clock                #    5.213 CPUs utilized            ( +-  0.45% )
>             14,423 context-switches          #    0.009 M/sec                    ( +-  4.28% )
>              2,710 cpu-migrations            #    0.002 M/sec                    ( +-  2.83% )

Hm, for these second round of measurements were you using 'perf stat 
-a -C ...'?

The most accurate method of measurement for such single-threaded 
workloads is something like:

	taskset 0x1 perf stat -a -C 1 --repeat 20 ...

this will bind your workload to CPU#0, and will do PMU measurements 
only there - without mixing in other CPUs or workloads.

Thanks,

	Ingo