netdev - Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling

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Message-ID: <20151023125211.GB17308@twins.programming.kicks-ass.net>
Date:	Fri, 23 Oct 2015 14:52:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Alexei Starovoitov <ast@...mgrid.com>, pi3orama <pi3orama@....com>,
	xiakaixu <xiakaixu@...wei.com>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org, daniel@...earbox.net,
	linux-kernel@...r.kernel.org, hekuang@...wei.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY
 maps trace data output when perf sampling

On Thu, Oct 22, 2015 at 06:28:22PM +0800, Wangnan (F) wrote:
> information to analysis when glitch happen. Another way we are trying to
> implement
> now is to dynamically turn events on and off, or at least enable/disable
> sampling dynamically because the overhead of copying those samples
> is a big part of perf's total overhead. After that we can trace as many
> event as possible, but only fetch data from them when we detect a glitch.

So why don't you 'fix' the flight recorder mode and just leave the data
in memory and not bother copying it out until a glitch happens?

Something like this:

lkml.kernel.org/r/20130708121557.GA17211@...ns.programming.kicks-ass.net

it appears we never quite finished that.
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