linux-kernel - Re: [PATCH v2 1/5] perf: Add a flags parameter to pmu txn interfaces

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Date:	Wed, 8 Apr 2015 08:40:54 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	mingo@...hat.com, Michael Ellerman <mpe@...erman.id.au>,
	dev@...yps.com, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 1/5] perf: Add a flags parameter to pmu txn interfaces

Peter Zijlstra [peterz@...radead.org] wrote:
| On Tue, Apr 07, 2015 at 05:34:55PM -0700, Sukadev Bhattiprolu wrote:
| > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
| > index 2b62198..4dc3d70 100644
| > --- a/include/linux/perf_event.h
| > +++ b/include/linux/perf_event.h
| > @@ -240,20 +240,27 @@ struct pmu {
| >  	 *
| >  	 * Start the transaction, after this ->add() doesn't need to
| >  	 * do schedulability tests.
| > +	 *
| > +	 * Optional.
| >  	 */
| > -	void (*start_txn)		(struct pmu *pmu); /* optional */
| > +#define PERF_PMU_TXN_ADD  0x1		/* txn to add/schedule event on PMU */
| 
| Please do not interleave these flags in the structure. Maybe place it
| near PERF_EVENT_TXN.

Ok.

| 
| > +	void (*start_txn)		(struct pmu *pmu, int flags);
| >  	/*
| >  	 * If ->start_txn() disabled the ->add() schedulability test
| >  	 * then ->commit_txn() is required to perform one. On success
| >  	 * the transaction is closed. On error the transaction is kept
| >  	 * open until ->cancel_txn() is called.
| > +	 *
| > +	 * Optional.
| >  	 */
| > -	int  (*commit_txn)		(struct pmu *pmu); /* optional */
| > +	int  (*commit_txn)		(struct pmu *pmu, int flags);
| >  	/*
| >  	 * Will cancel the transaction, assumes ->del() is called
| >  	 * for each successful ->add() during the transaction.
| > +	 *
| > +	 * Optional.
| >  	 */
| > -	void (*cancel_txn)		(struct pmu *pmu); /* optional */
| > +	void (*cancel_txn)		(struct pmu *pmu, int flags);
| >  
| >  	/*
| >  	 * Will return the value for perf_event_mmap_page::index for this event,
| 
| So (again), why also pass the flags to cancel/commit ?
| 
| The transaction state _has_ to already record it, otherwise it doesn't
| know if add/read are part of one.

I had replied to your earlier mail and added a Note to this patch
description. I was hesitating making more intrusive changes to PMUs
that don't care about the new txn type.

But, I agree, it is better to go ahead and update all PMUs to save
the state and check. Will do that in the next version.

Sukadev

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