From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Clark Williams <williams@redhat.com>
Cc: Stefan Roese <stefan.roese@gmail.com>, linux-rt-users@vger.kernel.org
Subject: Re: cyclictest better values with system load than without (OMAP3530 target)
Date: Fri, 29 Nov 2013 13:56:23 +0100 [thread overview]
Message-ID: <20131129125623.GB31099@linutronix.de> (raw)
In-Reply-To: <20131126101232.21636c8f@sluggy>
* Clark Williams | 2013-11-26 10:12:32 [-0600]:
>In my experience (on x86_64 mainly), that behavior (worse times when
>not under load) is due to the overhead of coming out of power-save/idle
>states. When you've got a big load on the system and all the cores are
>active, then the power-save logic and/or the idle logic doesn't kick in
>and devices aren't being powered down.
This is the case here, too. The overhead comming out of a deep power
state plus the invalidated caches.
>Do you know if your OMAP has power-save logic available? Alternatively
>do you know how expensive the idle mechanism is? Have you tried booting
>with idle=poll then measuring without a load?
idle=pull is x86 only. Disable the complete PM stuff should solve the
issue. You could go via arch_cpu_idle() to check what is used.
The idle routine should come either via cpuidle_idle_call() or arm_pm_idle().
>Clark
Sebastian
next prev parent reply other threads:[~2013-11-29 12:56 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-26 9:21 cyclictest better values with system load than without (OMAP3530 target) Stefan Roese
2013-11-26 14:21 ` Dmitry Lysenko
2013-11-26 19:14 ` Stefan Roese
2013-11-26 20:14 ` Tim Sander
2013-11-26 16:12 ` Clark Williams
2013-11-29 12:56 ` Sebastian Andrzej Siewior [this message]
2013-11-29 15:10 ` Carsten Emde
2013-11-29 16:36 ` Gilles Chanteperdrix
2013-11-29 16:58 ` Gilles Chanteperdrix
2013-11-29 17:36 ` Carsten Emde
2013-11-29 19:34 ` Gilles Chanteperdrix
2013-11-29 21:10 ` Carsten Emde
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