[lkml]   [2013]   [Nov]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 4/5] perf record: mmap output file - v5
Hi David,

On Tue, Nov 19, 2013 at 12:34 AM, David Ahern <> wrote:
> On 11/18/13, 5:24 PM, Namhyung Kim wrote:
>>>>> What now? Can we add the mmap path as an option?
>>>> I'd say an option is always a possibility, but someone please try
>>>> what happens if you use stupid large events (dwarf stack copies) on
>>>> PERF_COUNT_SW_PAGE_FAULTS (.period=1) while recording with mmap().
>>>> The other option is to simply disallow PERF_SAMPLE_STACK_USER for
>>>> that event.
>>>> Personally I think 8k copies for every event are way stupid anyway,
>>>> that's a metric ton of data at a huge cost.
>>> Well, with 1 khz sampling of a single threaded workload it's 8MB per
>>> second - that's 80 MB for 10 seconds profiling - not the end of the
>>> world.
>> We now use 4 khz sampling frequency by default, just FYI. :)
> I think Peter is asking about:
> perf record -e faults -c 1 --call-graph dwarf,8192 -a -- sleep 1
> And as expected it is a massive feedback spiraling out of control.

Ah, I missed that part - just blindly answered about the freq -
thinking he's talking about the default freq of perf record/top.

Anyway, for above case, I guess it won't affect much as stack usually
is in memory so no page fault will occur even recording with mmap
unless the system suffers from a high memory pressure, right?

But I agree that copying 8KB for each sample seems too large.


 \ /
  Last update: 2013-11-19 03:21    [W:0.088 / U:2.836 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site