linux-kernel - Re: [PATCH v3 04/25] clocksource: Add Owl timer

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Message-ID: <alpine.DEB.2.20.1702281953350.4007@nanos>
Date:   Tue, 28 Feb 2017 19:56:44 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andreas Färber <afaerber@...e.de>
cc:     Daniel Lezcano <daniel.lezcano@...aro.org>, arm@...nel.org,
        linux-arm-kernel@...ts.infradead.org, mp-cs@...ions-semi.com,
        96boards@...obotics.com, support@...aker.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/25] clocksource: Add Owl timer

On Tue, 28 Feb 2017, Andreas Färber wrote:
> This is a callback, which I thought is re-entrant.

It's not reentrant at least not on the same CPU. On a SMP machine this
function might be called concurrently on several cores (assumed that the
whole thing is replicated across cores).

> VAL changes when the timer is running, and CTL changes every time we
> enable the timer. We could call _reset() here, but then we would be
> initializing CMP twice, which again would be less performant then just
> setting the registers to their final values directly.

Makes sense.

Thanks,

	tglx