Re: [Xen-devel] [PATCH] VMX: avoid taking locks with irqs disabled

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 21/10/08 13:50, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> 
> I'm a bit curious why call funtion ipi is required here, or why
> rendezvous is required here. All the rendezvous stuff in current
> ipi function is just:
> a) cpu0 waits for all other cpus entering rendezvous loop, and
> then update master_stime
> b) other cpus enter loop and wait for cpu0 to update master_stime
> 
> Then each cpu continues with rest stuff independently. In this
> case, it seems enough to just ensure master_stime updated
> before sending softirq, and thus ipi is actually not required.
> Do I miss anything? :-)

We want to gather all timestamps as close together as possible. Dan measured
that this produced vastly less system-time skew across CPUs. Hence we do all
the stamp gathering in IRQ context.

 -- Keir



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