Messages in this thread | | | Date | Fri, 16 Nov 2007 07:13:32 +0100 | From | Ingo Molnar <> | Subject | Re: x86: disable preemption in delay_tsc() |
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* Andrew Morton <akpm@linux-foundation.org> wrote:
> > > x86: disable preemption in delay_tsc() > > > > > > Marin Mitov points out that delay_tsc() can misbehave if it is > > > preempted and rescheduled on a different CPU which has a skewed > > > TSC. Fix it by disabling preemption. > > > > > > > this worries me.. this appears to effectively disable preemption > > during udelay() and mdelay() loops... which are very obvious latency > > inducers. > > > > Now you can argue that if you're preemptible you should have used > > msleep() and co, and I'll totally buy that. > > > > > > Maybe we should just check if we're still on the same cpu or > > something, or have a cheap way to pin a process to a cpu.... but > > both are longer term solutions. > > Yes, we can do better. > > But this bug can cause very rare failures in probably a large number > of device drivers on a minorty of machines. Ugly. So I felt it best > to plug it fast while people think about more sophisticated fixes.
how about using usleep() transparently if high-res timers are active and we have !preempt_count()? That would be a sufficient solution and would avoid all the calibration and per-cpu-ness problems.
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