Re: [PATCH][RESEND]RE: [Xen-devel] [PATCH] Fix softlockup issue after vcpu hotplug

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 2/2/07 01:23, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> wrote:

> Fair point! I must have compared two 2.6.16 trees...
> 
> Well, that is interesting. I have no idea how SCHED_FIFO/sched_priority=99
> interacts with timer wheels and/or tickless idle modes. I wonder why this
> was changed at all? Perhaps a question for lkml...

Odder still, the softlockup threads are SCHED_FIFO/99 in 2.6.16 too. So the
main change is that rather than an explicit sleep of one second, the thread
now sleeps as TASK_INTERRUPTIBLE. I wonder how it gets kicked back to
TASK_RUNNING?

http://lwn.net/Articles/173648/ is worrying since it seems to state that the
patch intends to make the thread timer-interrupt driven rather than softirq
timer driven. If that means it is jiffy-ticker driver, then perhaps the
softlockup module is incompatible with tickless idle mode (no-idle-hz).

I should probably ask Ingo about it.

 -- Keir



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