Messages in this thread | | | Date | Thu, 15 Nov 2007 19:52:34 -0800 | From | Andrew Morton <> | Subject | Re: x86: disable preemption in delay_tsc() |
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On Thu, 15 Nov 2007 19:41:16 -0800 Arjan van de Ven <arjan@infradead.org> wrote:
> On Thu, 15 Nov 2007 04:00:47 GMT > Linux Kernel Mailing List <linux-kernel@vger.kernel.org> wrote: > > > Gitweb: > > http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=35d5d08a085c56f153458c3f5d8ce24123617faf > > Commit: 35d5d08a085c56f153458c3f5d8ce24123617faf Parent: > > 7eea436433b7b18045f272562e256976f593f7c0 Author: Andrew Morton > > <akpm@linux-foundation.org> AuthorDate: Wed Nov 14 17:00:41 2007 -0800 > > Committer: Linus Torvalds <torvalds@woody.linux-foundation.org> > > CommitDate: Wed Nov 14 18:45:44 2007 -0800 > > > > 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.
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