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Date: Mon, 30 Aug 2010 20:35:58 +0100
From: Matt Fleming <matt@console-pimps.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Zhang Rui <rui.zhang@intel.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
        Robert Richter <robert.richter@amd.com>,
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        Don Zickus <dzickus@redhat.com>, Cyrill Gorcunov <gorcunov@gmail.com>,
        Len Brown <lenb@kernel.org>, Matthew Garrett <mjg59@srcf.ucam.org>
Subject: Re: [RFC][PATCH 3/5] perf: Add hrtimer code for PMI-less hardware
 counters
Message-ID: <20100830193558.GE24828@console-pimps.org>
References: <cover.1283123521.git.matt@console-pimps.org>
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On Mon, Aug 30, 2010 at 04:12:24PM +0200, Peter Zijlstra wrote:
> On Mon, 2010-08-30 at 14:27 +0100, Matt Fleming wrote:
> 
> > I'm lost. Is it possible to do this patch entirely in userspace? How do
> > we periodically sample the counters if it's not being done in the
> > kernel?
> 
> perf_event_attr leader = {
>  .type = PERF_TYPE_SOFTWARE,
>  .config = PERF_COUNT_SW_TASK_CLOCK,
>  .sample_period = xxx,
>  .sample_type = PERF_SAMPLE_READ|...,
>  .read_format = PERF_FORMAT_GROUP,
> };
> 
> perf_event_attr counter = {
>  .type = PERF_TYPE_HARDWARE,
>  .config = PERF_COUNT_HW_CPU_CYCLES,
> };
>  
> leader_fd = sys_perf_event_open(&leader, pid, cpu, 0, 0);
> counter_fd = sys_perf_event_open(&counter, pid, cpu, leader_fd, 0);
> 
> Which gives you a group of 2 events, one software timer that samples,
> one hardware counter that only counts.

Aha. OK, thanks! I'll respin this.