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

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Date:	Wed, 15 Apr 2015 18:21:11 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Kan Liang <kan.liang@...el.com>, acme@...nel.org,
	eranian@...gle.com, andi@...stfloor.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 1/6] perf,core: allow invalid context events to be
 part of sw/hw groups

On Wed, Apr 15, 2015 at 06:15:28PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 15, 2015 at 03:56:11AM -0400, Kan Liang wrote:
> > From: Kan Liang <kan.liang@...el.com>
> > 
> > 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 perf.data (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?

Without the patch you can't mix uncore and cpu core events in the same
group.

Collecting uncore in PMIs is useful, for example to get memory
bandwidth over time.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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