Re: [Xen-devel] [PATCH] Pin vcpu for VMX domain

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 8 Feb 2006, at 12:58, Jiang, Yunhong wrote:

> I'm not sure if it will has some corner case, and hope your
> clarification for it.
> considering following situation, assume the VMX switch from cpu 0->cpu1
> 1) on cpu0, the timer interrupt happened, so timer_softirq_action is
> called, the pit_timer_fn is called, and in pit_timer_fn, it will try to
> set the  pit timer again.
> 2) before pit_timer_fn set the pit timer on cpu0, the stop_timer is
> called on cpu1 on vmx_reinstall_timers.
> 3) after stop_timer finished, the pit_timer_fn on cpu0 set the ac_timer
> on cpu0.
>
> on this situation, the stop_timer on cpu1 will has no effect. And then
> the init_timer may cause error situation.
>
> In fact, I think the old patch itself is not safe on this situation,
> since the stop_timer is called on IPI interrupt , which may run when 
> the
> pit_timer_fn is running.
Good point. I'll have to add a migrate_timer() function I think, that 
does the migration atomically.
That'll save you the hassle of stop/init/reactivate as well.

 -- Keir


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