Re: [PATCH 0/6] perf core: Read from overwrite ring buffer

[Alexei Starovoitov]

On Fri, Jan 22, 2016 at 12:13:48PM +0000, Wang Nan wrote:
> This is v2 of this series.
> 
> Compare with v1:
> 
> Fixes several bugs in v1.
> 
> Corresponsing perf has finished and can be found from:
> 
>  https://git.kernel.org/cgit/linux/kernel/git/pi3orama/linux.git/ 
>  branch: perf/overwrite-benchmark
> 
> Some benchmarking results can be found from [1].
> 
> Summary:
> 
> On a PC with Intel E5-2640 0 @ 2.50GHz CPU, execute close(-1) 3000000
> times, capture raw_syscalls:* with perf into overwrite ring buffer,
> check total time (in us):
> 
>              MEAN           STDVAR
> BASE     :  879870.81      11913.13
> RAWPERF  : 2603854.7      706658.4
> WRTBKWRD : 2313301.220      6727.957
> TAILSIZE : 2383051.860      5248.061
> RAWOVWRT : 2315273.180      5221.025
> RAWOVWRT*: 2323970.45       5103.39 
> 
> Where:
> BASE: don't use perf at all.
> RAWPERF: use non-overwrite ring buffer, perf collects all data,
> 	 write to /dev/null
> WRTBKWRD: Use backward writing ring buffer, write from tail to head,
>           never wakeup perf, collect data when exiting.
> TAILSIZE: Use tailsize ring buffer, pad 8 bytes for the size of the
>           record for each event, never wakeup perf, collect data when
> 	  exiting.
> RAWOVWRT: Use raw overwrite ring buffer, never wakeup perf, don't
>           collect data at all.
> RAWOVWRT*: Same as RAWOVWRT, without this patchset.
> 
> The benchmarking results shows WRTBKWRD is good enough. I suggest not
> to implement TAILSIZE and tail-header ring buffer.

yes. just drop patch 6.

> I will post the result on a smartphone next week.

great. would be interesting comparison.
overall I think it looks good.