linux-kernel - Re: [PATCH 3/6] perf record: add time-of-day option

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Date:	Tue, 01 Mar 2011 16:35:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <daahern@...co.com>
Cc:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	acme@...stprotocols.net, mingo@...e.hu, fweisbec@...il.com,
	paulus@...ba.org, tglx@...utronix.de
Subject: Re: [PATCH 3/6] perf record: add time-of-day option

On Tue, 2011-03-01 at 07:35 -0700, David Ahern wrote:
> 
> On 03/01/2011 07:29 AM, Peter Zijlstra wrote:
> 
> >> +/* add a sample to the event stream based on user request */
> >> +static int perf_event_generate_sample(struct perf_event *event)
> >> +{
> >> +       struct perf_sample_data data;
> >> +       struct pt_regs regs;
> >> +
> >> +       perf_fetch_caller_regs(&regs);
> >> +       event->pmu->read(event);
> >> +       perf_sample_data_init(&data, 0);
> >> +       data.period = event->hw.last_period;
> >> +       perf_event_output(event, 0, &data, &regs);
> >> +
> >> +       return 0;
> >> +}
> > 
> > I'm not quite sure why you need this.. 
> > 
> 
> periodic samples are generated after the specified period. I want the
> first sample immediately and the remainder based on the set period.
> 
> So generically, how do you get the first sample into the event stream
> and let the others happen based on the timer? I need not only the
> counter value but also the perf_clock timestamp that comes from the
> SAMPLE_TIME attribute.

Again, why?

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