Re: [PATCH 0/5] perf core: Read from overwrite ring buffer

[Alexei Starovoitov]

On Mon, Jan 25, 2016 at 08:33:48AM +0000, Wang Nan wrote:
> This is the v3 of this series. Compare with v2, tailsize method is
> removed, ioctl command PERF_EVENT_IOC_PAUSE_OUTPUT is changed to
> _IOW('$', 9, __u32) since it has an input value, commit message
> is slightly adjusted.
> 
> New test result on ARM64 is below (x86_64 result is copied from previous
> email, test method is described in previous version [1]):
> 
>                        x86_64        |       ARM64
>               -----------------------+---------------------
>                 MEAN         STDVAR  |    MEAN       STDVAR
>    BASE     :  879870.81   11913.13  |  808302.67   6951.47
>    RAWPERF  : 2603854.70  706658.40  | 3461675.12  54075.69
>    WRTBKWRD : 2313301.22    6727.96  | 3350177.98  23125.48
>    TAILSIZE : 2383051.86    5248.06  | 3556496.56  24802.17
>    RAWOVWRT : 2315273.18    5221.03  | 3458767.49  41560.32
>    RAWOVWRT*: 2323970.45    5103.39  | 3438967.06  34095.83
> 
> ARM64 platform is a smartphone with 8 Hisilicon arm64 cores
> (big/little).
> 
> Benckmarking result on both architechure support removing tailsize
> method because its performance penalty is higher than WRTBKWRD. Also, it
> seems we don't need to consider tailheader method (putting whole header
> at the end of records, kernel write to the ring buffer from beginning to
> end), because the above result shows WRTBKWRD and RAWOVWRT are similar,
> and tailheader is impossible to outperform RAWOVWRT in theory.

looks ok to me.