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Message-ID: <970896.1567893622@turing-police>
Date: Sat, 07 Sep 2019 18:00:22 -0400
From: "Valdis Klētnieks" <valdis.kletnieks@...edu>
To: Theodore Dubois <tbodt@...gle.com>
Cc: a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org,
kernelnewbies@...nelnewbies.org
Subject: Re: perf_event wakeup_events = 0
On Sat, 07 Sep 2019 09:14:49 -0700, Theodore Dubois said:
> If I���m reading this right, this is a sampling event which overflows 4000
> times a second. But perf then does a poll call which wakes up on this FD with
> POLLIN after 1.637 seconds, instead of 0.00025 seconds.
No, it *takes a sample* 4,000 times a second. For instance, number of cache line
misses since the last sample. You get an overflow when the counter wraps because
there have been more than 2^32 events since you read the counter.
At least that's my understanding of it.
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