linux-kernel - Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions

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Message-ID: <20151217184255.GI6344@twins.programming.kicks-ass.net>
Date:	Thu, 17 Dec 2015 19:42:55 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Suzuki K. Poulose" <suzuki.poulose@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mark.rutland@....com, punit.agrawal@....com, arm@...nel.org
Subject: Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions

On Thu, Dec 17, 2015 at 05:49:12PM +0000, Suzuki K. Poulose wrote:
> This patch adds the transaction hooks for CCI PMU, which can be
> later exploited to amortise the cost of writing the counters for
> CCI-500 PMU.
> 
> We keep track of only the 'ADD' transactions. While we are in a
> transaction, we keep track of the indices allocated for the events
> and delay the following operations until the transaction is committed.
>  1) Programming the event on the counter
>  2) Enabling the counter
>  3) Setting the period for the event.

So that's not really what the txn interface is for, its meant to
amortize event scheduling.

The above doesn't look like it has a failure case, in which case you can
achieve the same simpler, using pmu::pmu_{dis,en}able().

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