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From: "Valdis Klētnieks" <valdis.kletnieks@vt.edu>
To: Theodore Dubois <tbodt@google.com>
Cc: kernelnewbies@kernelnewbies.org, a.p.zijlstra@chello.nl,
	linux-kernel@vger.kernel.org
Subject: Re: perf_event wakeup_events = 0
Date: Sat, 07 Sep 2019 18:00:22 -0400
Message-ID: <970896.1567893622@turing-police> (raw)
In-Reply-To: <123C743E-C322-45DB-8796-BF6B6EE9CA80@google.com>

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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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Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAN3rvwA+Dnqj4O79f6rNfO50VjbAC3YwJ7CW2ze2aBLzkSJRgQ@mail.gmail.com>
2019-09-07 13:40 ` Valdis Klētnieks
     [not found]   ` <123C743E-C322-45DB-8796-BF6B6EE9CA80@google.com>
2019-09-07 22:00     ` Valdis Klētnieks [this message]
2019-09-07 22:45     ` Valdis Klētnieks

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