Messages in this thread | | | Date | Thu, 15 Dec 2005 17:52:02 -0800 (PST) | From | Zwane Mwaikambo <> | Subject | Re: [PATCH] ia64: disable preemption in udelay() |
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On Thu, 15 Dec 2005, Luck, Tony wrote:
> On Wed, Dec 14, 2005 at 03:25:26PM -0800, hawkes@sgi.com wrote: > > Sending this to a wider audience: > > > > The udelay() inline for ia64 uses the ITC. If CONFIG_PREEMPT is enabled > > and the platform has unsynchronized ITCs and the calling task migrates > > to another CPU while doing the udelay loop, then the effective delay may > > be too short or very, very long. > > > > The most simple fix is to disable preemption around the udelay looping. > > The downside is that this inhibits realtime preemption for cases of long > > udelays. One datapoint: an SGI realtime engineer reports that if > > CONFIG_PREEMPT is turned off, that no significant holdoffs are > > are attributed to udelay(). > > > > I am reluctant to propose a much more complicated patch (that disables > > preemption only for "short" delays, and uses the global RTC as the time > > base for longer, preemptible delays) unless this patch introduces > > significant and unacceptable preemption delays. > > Stuck between a rock and the proverbial hard place. > > I think that the more complex patch is needed though. If some crazy > driver has a pre-emptible udelay(10000), then you really don't want > to spin for that long without allowing preemption.
If it's a preemptible sleep period it should just use msleep. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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