From: jbarnes@sgi.com (Jesse Barnes)
To: linux-ia64@vger.kernel.org
Subject: Re: udelay() & preemption & drifty ITCs
Date: Sun, 23 Nov 2003 22:39:29 +0000 [thread overview]
Message-ID: <marc-linux-ia64-106962729019919@msgid-missing> (raw)
In-Reply-To: <marc-linux-ia64-106955914311295@msgid-missing>
On Sat, Nov 22, 2003 at 09:45:25PM -0600, Jack Steiner wrote:
> I may be overlooking something, but isnt there a problem
> with the udelay() function on IA64 platforms with drifty ITCs
> when preemption is enabled.
>
> The function uses the ITC for timing. If preemption occurs & the process
> migrates to a different cpu with a much larger ITC value, it
> seems like the delay may be satisfied too quickly.
Yep, it appears so. I guess we need a 'preempt_disable/disable()' pair
around the itc access. Of course, callers under a spinlock are already
protected, so maybe exposure to this problem isn't that large?
Jesse
next prev parent reply other threads:[~2003-11-23 22:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-11-23 3:45 udelay() & preemption & drifty ITCs Jack Steiner
2003-11-23 22:39 ` Jesse Barnes [this message]
2003-11-24 21:00 ` Jesse Barnes
2003-11-24 21:13 ` Jesse Barnes
2003-11-24 21:25 ` Jesse Barnes
2003-11-24 22:01 ` Jack Steiner
2003-11-24 22:21 ` Jesse Barnes
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