Re: [PATCH V2 1/6] perf,core: allow invalid context events to be part of sw/hw groups

From: Peter Zijlstra
Date: Wed Apr 15 2015 - 12:15:57 EST

On Wed, Apr 15, 2015 at 03:56:11AM -0400, Kan Liang wrote:
> From: Kan Liang <kan.liang@xxxxxxxxx>
> The pmu marked as perf_invalid_context don't have any state to switch on
> context switch. Everything is global. So it is OK to be part of sw/hw
> groups.
> In sched_out/sched_in, del/add must be called, so the
> perf_invalid_context event can be disabled/enabled accordingly during
> context switch. The event count only be read when the event is already
> sched_in.
> However group read doesn't work with mix events.
> For example,
> perf record -e '{cycles,uncore_imc_0/cas_count_read/}:S' -a sleep 1
> It always gets EINVAL.
> This patch set intends to fix this issue.
> perf record -e '{cycles,uncore_imc_0/cas_count_read/}:S' -a sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.202 MB (12 samples) ]
> This patch special case invalid context events and allow them to be part
> of sw/hw groups.

I don't get it. What, Why?
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