Re: [PATCH v4 3/7] perf tools: Enable overwrite settings

["Wangnan (F)" <wangnan0@huawei.com>]

On 2016/5/25 2:40, Arnaldo Carvalho de Melo wrote:
> Em Tue, May 24, 2016 at 02:29:00AM +0000, Wang Nan escreveu:
>> This patch allows following config terms and option:
>>
>> Globally setting events to overwrite;
>>
>>   # perf record --overwrite ...
>>
>> Set specific events to be overwrite or no-overwrite.
>>
>>   # perf record --event cycles/overwrite/ ...
>>   # perf record --event cycles/no-overwrite/ ...
> So, based on this chunk of documentation in this patch:
>
> <quote>
> Perf dumps data from overwritable ring buffer when switching output (see
> --switch-output) and before terminate.
> </>
>
> I tried:
>
> No --overwrite:
>
>    # perf record -e syscalls:*enter_nanosleep* usleep 1
>    [ perf record: Woken up 1 times to write data ]
>    [ perf record: Captured and wrote 0.019 MB perf.data (1 samples) ]
>    # perf evlist -v
>    syscalls:sys_enter_nanosleep: type: 2, size: 112, config: 0x132, { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CPU|PERIOD|RAW, disabled: 1, inherit: 1, mmap: 1, comm: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1
>    # Tip: use 'perf evlist --trace-fields' to show fields for tracepoint events
>    # perf script
>            usleep 29416 [002] 220099.782982: syscalls:sys_enter_nanosleep: rqtp: 0x7ffc21f73cc0, rmtp: 0x00000000
>
> Now I went on to try this new --overwrite thing:
>
>    # perf record --overwrite -e syscalls:*enter_nanosleep* usleep 1
>    [ perf record: Woken up 1 times to write data ]
>    [ perf record: Captured and wrote 0.019 MB perf.data ]
>    # perf evlist -v
> syscalls:sys_enter_nanosleep: type: 2, size: 112, config: 0x132, { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CPU|PERIOD|RAW, disabled: 1, inherit: 1, mmap: 1, comm: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, write_backward: 1
>    # Tip: use 'perf evlist --trace-fields' to show fields for tracepoint events
>    # perf script
>    #
>
> So it hasn't recorded anything at anytime, i.e. I expected, based on the
> documentation provided, that it would get what was in its buffer, to be written,
> i.e. the single "syscalls:sys_enter_nanosleep" event that took place in that
> workload.
>
> So I'm now trying it together with --switch-output, but I just get one
> timestamp suffixed perf.data file, empty, without that event that I know took
> place.
>
> Care to ellaborate here?

Sorry, you need to apply patch 3/7 - 5/7 to enable operations described 
here.

I'll reorder these patches and send again, but some important patch 
would become
untestable until patch 3/7 get applied. I'll try to add a test case for 
them.

Thank you.