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

From: Peter Zijlstra <peterz@infradead.org>
To: "Wangnan (F)" <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>,
	pi3orama <pi3orama@163.com>, xiakaixu <xiakaixu@huawei.com>,
	davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
	masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org,
	daniel@iogearbox.net, linux-kernel@vger.kernel.org,
	hekuang@huawei.com, netdev@vger.kernel.org
Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling
Date: Fri, 23 Oct 2015 14:52:11 +0200	[thread overview]
Message-ID: <20151023125211.GB17308@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <5628BA46.8060307@huawei.com>

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@twins.programming.kicks-ass.net

it appears we never quite finished that.