linux-kernel - Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

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Message-ID: <20160804142853.GO6862@twins.programming.kicks-ass.net>
Date:	Thu, 4 Aug 2016 16:28:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Brendan Gregg <bgregg@...flix.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
	Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote:

> As for pmu tracepoints: if I were to instrument it (although I wasn't
> planning to), I'd put a tracepoint in perf_event_overflow() called
> "perf:perf_overflow", with the same arguments. That could then be used
> for all PMU overflow events, without needing to add specific
> tracepoints. 

Could we not teach BPF to replace event->overflow_handler and inject
itself there?

We don't currently have nice interfaces for doing that, but it should be
possible to do I think. We already have the indirect function call, so
injecting ourself there has 0 overhead.