Re: Fwd: filtering perf itself

[Brendan Gregg <brendan.d.gregg@gmail.com>]

On Mon, Jul 7, 2014 at 11:44 AM, David Ahern <dsahern@gmail.com> wrote:
> On 7/7/14, 12:38 PM, Brendan Gregg wrote:
>>
>> G'Day perf users,
>>
>> Is there a way to filter perf from tracing itself?
>>
>> Here's an idle system:
>>
>> # ./perf record -e syscalls:sys_enter_read -a sleep 5
>> [ perf record: Woken up 2 times to write data ]
>> [ perf record: Captured and wrote 0.569 MB perf.data (~24864 samples) ]
>> # ./perf record -e syscalls:sys_enter_write -a sleep 5
>> [ perf record: Woken up 0 times to write data ]
>> [ perf record: Captured and wrote 150.381 MB perf.data (~6570251 samples)
>> ]
>>
>> Note the disparity. perf is capturing its own writes, creating a feedback
>> loop.
>
>
> Not a filter, but works around the problem using mmap'ed output file:
>
> https://github.com/dsahern/linux/commit/ae2d7010256f5a5b247fb4df9f764a911a34a2f3
>

Ah, thanks David, that should work! Looking forward to having this
patch included.

Brendan

-- 
http://www.brendangregg.com