From: Thomas Gleixner <tglx@linutronix.de>
To: Doug Anderson <dianders@chromium.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>,
Tomasz Figa <t.figa@samsung.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Chirantan Ekbote <chirantan@chromium.org>,
David Riley <davidriley@chromium.org>,
olof@lixom.net, linux-samsung-soc@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] clocksource: exynos_mct: Optimize register reads with ldmia
Date: Wed, 4 Jun 2014 20:05:47 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.10.1406042004140.3319@nanos> (raw)
In-Reply-To: <1401903034-20074-3-git-send-email-dianders@chromium.org>
On Wed, 4 Jun 2014, Doug Anderson wrote:
> As we saw in (clocksource: exynos_mct: cache mct upper count), the
> time spent reading the MCT shows up fairly high in real-world
> profiles. That means that it's worth some optimization.
>
> We get a roughly 10% speedup in userspace gettimeofday() by using an
> ldmia to read the two halfs of the MCT. That seems like a worthwhile
> thing to do.
>
> Before: 1173084 us for 1000000 gettimeofday in userspace
> After: 1045674 us for 1000000 gettimeofday in userspace
>
> NOTE: we could actually do better than this if we really wanted to.
> Technically we could register the clocksource as a 32-bit timer and
> only use the "lower" half. Doing so brings us down to 1014429 us for
> 1000000 gettimeofday in userspace (and doesn't even require assembly
> code). That would be an alternative to this change.
I was about to ask exactly that question: What's the advantage of the
64 bit dance there? AFAICT nothing.
Thanks,
tglx
next prev parent reply other threads:[~2014-06-04 18:05 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-04 17:30 [PATCH 1/3] clocksource: exynos_mct: Fix ftrace Doug Anderson
2014-06-04 17:30 ` [PATCH 2/3] clocksource: exynos_mct: cache mct upper count Doug Anderson
2014-06-05 7:55 ` Vincent Guittot
2014-06-05 17:14 ` Doug Anderson
2014-06-04 17:30 ` [PATCH 3/3] clocksource: exynos_mct: Optimize register reads with ldmia Doug Anderson
2014-06-04 18:05 ` Thomas Gleixner [this message]
2014-06-04 18:49 ` Doug Anderson
2014-06-05 11:18 ` Tomasz Figa
2014-06-05 18:21 ` Doug Anderson
2014-06-12 16:53 ` Doug Anderson
2014-06-15 21:18 ` [PATCH 1/3] clocksource: exynos_mct: Fix ftrace Daniel Lezcano
2014-06-16 4:40 ` Doug Anderson
2014-06-16 8:52 ` Daniel Lezcano
2014-06-16 16:35 ` Doug Anderson
2014-06-17 12:13 ` Daniel Lezcano
2014-06-19 17:07 ` Doug Anderson
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