From: daniel.lezcano@linaro.org (Daniel Lezcano)
To: linux-arm-kernel@lists.infradead.org
Subject: cpu_relax in busy loops question
Date: Wed, 01 Feb 2012 12:34:29 +0100 [thread overview]
Message-ID: <4F292345.8070800@linaro.org> (raw)
Hi Linus,
While looking at the drivers/mfd/db8500-prcmu.c file I noticed:
595 /* Grab the HW semaphore. */
596 while ((readl(PRCM_SEM) & PRCM_SEM_PRCM_SEM) != 0)
597 cpu_relax();
I was wondering why is cpu_relax needed here as readl does a memory
barrier ? I thought the cpu_relax function was related to the x86 to
consume less power with an optimization of the "rep nop" loops or/and do
a memory barrier.
Should a busy-loop be always with cpu_relax ?
Thanks
-- Daniel
--
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next reply other threads:[~2012-02-01 11:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-01 11:34 Daniel Lezcano [this message]
2012-02-01 20:17 ` cpu_relax in busy loops question Linus Walleij
2012-02-02 8:47 ` Daniel Lezcano
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