Date: Mon, 7 Jul 2014 11:13:08 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Christopher Covington <cov@codeaurora.org>
Cc: Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] RFC: perf: Make overflow signals inheritable
Message-ID: <20140707091308.GH6758@twins.programming.kicks-ass.net>
References: <1403727129-20665-1-git-send-email-cov@codeaurora.org>
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On Wed, Jun 25, 2014 at 04:12:09PM -0400, Christopher Covington wrote:
> In order to get a signal from the perf events framework (use an
> "event_limit"), one must not not only call perf_event_open() with the
> appropriate sample_period, watermark, and wakeup_watermark values,
> but also set the FASYNC flag on the resulting file descriptor with
> fcntl().=20

Tell me more; why are you wanting this?

> If the inherit attribute is also set, one would expect child
> tasks to cause signals like their parents. They don't, though,
> because their FASYNC setting isn't set (and can't be by the user
> since only the parent has a file descriptor). To fix this, allow the
> parent's FASYNC value to be passed along to child events when the
> inherit attribute is set. Overflow counts are still per process and
> per CPU.

There's more issues though; the comment you deleted isn't explicit about
this (it maybe should have been).

This would mean the inherited children would get signals; they might not
be expecting them.

When they do get a signal, they should be calling IOC_REFRESH to re-arm
the signal, but that explicitly doesn't work for inherited events. Which
leads me to believe you didn't actually test this.

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