Messages in this thread | | | Date | Tue, 9 Sep 2014 18:08:39 -0700 | Subject | Re: [PATCH] perf, tools: Add PERF_PID | From | Brendan Gregg <> |
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On Tue, Sep 9, 2014 at 5:03 PM, Andi Kleen <andi@firstfloor.org> wrote: > From: Andi Kleen <ak@linux.intel.com> > > It's currently difficult to filter out perf itself using a filter. > This can give cascading effects during IO tracing when the IO > perf does itself causes more trace output. > > The best way to filter is to use the pid. But it's difficult to get the pid > of perf without using hacks. > > Add a PERF_PID meta variable to the perf filter that contains the current pid. > > With this patch the following works > > % perf record -e syscalls:sys_enter_write -a --filter 'common_pid != PERF_PID' ... > > This won't work for more complex perf pipe lines with multiple processes, > but at least solves the problem nicely for a single perf.
Thank you, this will be handy. I tested it and it works.
It will mean I can avoid hacks like this: https://github.com/brendangregg/perf-tools/blob/d30e8a1a9f136d532ba78c6d48aedb99dc316be9/syscount#L144
I think it's unrelated to this patch, but the very next test I tried didn't work as expected:
# perf record -e 'syscalls:sys_enter_*' --filter 'common_pid != PERF_PID' -a sleep 5
It only filters the last event from the wildcard expansion, leaving write() unfiltered. Looks like it's because parse_filter() is only setting the filter for perf_evlist__last(), instead of doing an evlist__for_each(). How best to deal with this can be addressed in a separate patch later.
Brendan
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