Re: [Xen-devel] [PATCH, RFC] x86/HVM: batch vCPU wakeups

[Tim Deegan <tim@xxxxxxx>]

At 23:37 +0100 on 09 Sep (1410302243), Andrew Cooper wrote:
> >> +void cpu_raise_softirq_batch_finish(void)
> >> +{
> >> +    unsigned int cpu, this_cpu = smp_processor_id();
> >> +    cpumask_t *mask = &per_cpu(batch_mask, this_cpu);
> > Again, this_cpu()?
> 
> ...But disagree here.  Multiple uses of this_cpu($FOO) cannot be
> coalesced due to RELOC_HIDE() deliberately preventing optimisation.  For
> multiple uses, pulling it out by pointer to start with results in rather
> more efficient code.

I wasn't questioning the pointer, but to the use of per_cpu(...,
this_cpu) instead of this_cpu(...).  Both of those involve a
RELOC_HIDE().

Anyway, it's pretty clear from your and Jan's replies that multiple
this_cpu() invocations are slower -- thanks for the clarification!

Tim.

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