From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: udelay() broken for SMP cores?
Date: Wed, 21 Apr 2010 08:22:43 +0100 [thread overview]
Message-ID: <20100421072243.GA913@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <4BCE9E8B.2070103@codeaurora.org>
On Tue, Apr 20, 2010 at 11:43:23PM -0700, Saravana Kannan wrote:
>
>>> I looked at arch/arm/lib/delay.S and it looks like __udelay and
>>> __const_udelay won't work correctly for SMP cores. The code just uses
>>> the loops_per_jiffy variable instead of the per-CPU loops per jiffy data.
>>>
>>> Is anyone already working on a fix for that? If not, I can fix it up in
>>> a way that's hopefully palatable to the community.
>>
>
>> If you have case where individual CPUs are running at different speed and different
>> Tick rate then only this can make difference.
>
> Yes. I was talking about the case where the CPUs could be running at
> different speeds.
We don't support that; if we did, we'd have to disable preempt for every
call to mdelay/udelay to ensure that the thread is locked to a particular
CPU. I suspect that will (a) destroy RT scheduling preformance (b)
increase preempt latency to an undesirable extent.
next prev parent reply other threads:[~2010-04-21 7:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-21 2:19 udelay() broken for SMP cores? Saravana Kannan
2010-04-21 4:56 ` Shilimkar, Santosh
2010-04-21 6:43 ` Saravana Kannan
2010-04-21 7:22 ` Russell King - ARM Linux [this message]
2010-04-21 9:39 ` skannan at codeaurora.org
2010-04-21 9:50 ` Russell King - ARM Linux
2010-04-21 9:58 ` Gilles Chanteperdrix
2010-04-21 10:00 ` Jamie Lokier
2010-04-21 19:29 ` Russell King - ARM Linux
2010-04-21 19:52 ` Jamie Lokier
2010-04-21 20:21 ` Russell King - ARM Linux
2010-04-21 20:47 ` Jamie Lokier
2010-04-21 20:57 ` Russell King - ARM Linux
2010-04-22 0:14 ` Jamie Lokier
2011-01-08 23:24 ` Russell King - ARM Linux
2010-04-21 10:31 ` skannan at codeaurora.org
2010-04-21 19:33 ` Russell King - ARM Linux
2010-04-21 23:47 ` Saravana Kannan
2010-04-23 9:00 ` Pavel Machek
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