linux-kernel - Re: [[PATCH v6 09/10] powerpc/perf/hv-24x7: Use PMU_TXN

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Message-ID: <1441703275.7601.5.camel@ellerman.id.au>
Date:	Tue, 08 Sep 2015 19:07:55 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [[PATCH v6 09/10] powerpc/perf/hv-24x7: Use PMU_TXN_READ
 interface

On Thu, 2015-09-03 at 20:07 -0700, Sukadev Bhattiprolu wrote:
> The 24x7 counters in Powerpc allow monitoring a large number of counters
> simultaneously. They also allow reading several counters in a single
> HCALL so we can get a more consistent snapshot of the system.
> 
> Use the PMU's transaction interface to monitor and read several event
> counters at once. The idea is that users can group several 24x7 events
> into a single group of events. We use the following logic to submit
> the group of events to the PMU and read the values:
> 
> 	pmu->start_txn()		// Initialize before first event
> 
> 	for each event in group
> 		pmu->read(event);	// Queue each event to be read
> 
> 	pmu->commit_txn()		// Read/update all queuedcounters
> 
> The ->commit_txn() also updates the event counts in the respective
> perf_event objects.  The perf subsystem can then directly get the
> event counts from the perf_event and can avoid submitting a new
> ->read() request to the PMU.
> 
> Thanks to input from Peter Zijlstra.
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/perf/hv-24x7.c |  166 ++++++++++++++++++++++++++++++++++++++++++-

This looks fine to me from an arch perspective. I assume the whole series can
go via tip-something?

Acked-by: Michael Ellerman <mpe@...erman.id.au>

cheers


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