Re: [RFC resend] Perf: Trigger and dump sample info to perf.data from user space ring buffer
From: David Ahern
Date: Mon Sep 21 2015 - 23:28:06 EST
On 9/21/15 9:16 PM, Yunlong Song wrote:
[Problem Background]
We want to run perf in daemon mode and collect the traces when the exception
(e.g., machine crashes, app performance goes down) appears. Perf may run for a
long time (from days to weeks or even months), since we do not know when the
exception will appear at all, however it will appear at some time (especially
for a beta product). If we simply use âperf recordâ as usual, here come two
problems as time goes by: 1 there will be large amounts of IOs created for writing
perf.data which may affects the performance a lot; 2 the size of perf.data will
be larger and larger as well. Although we can use eBPF to reduce the traces in
normal case, but in our case, the perf runs in daemon mode for a long time and
that will accumulate the traces as time goes by.
This is a perf-based scheduling daemon I wrote a few years ago:
https://github.com/dsahern/linux/blob/perf/full-monty/tools/perf/schedmon.c
It solves a similar problem by holding the last N-seconds or M-bytes of
events in memory. When something of significance happens it is notified
to dump events to a file. The events are scheduling tracepoints but
could easily be anything else.
David
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