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SubjectRe: [PATCH 8/9] KVM, VMX: Add support for guest/host-only profiling
On 10/04/2011 01:17 PM, Gleb Natapov wrote:
> >
> > I mean, CONFIG_KVM&& !CONFIG_PERF_EVENTS is an unlikely
> > combination. If you're using kvm, you usually want PERF_EVENTS.
> >
> Who knows. Think about someone building appliance with embedded KVM and
> trying to achieve minimal code footprint.

Saving a few dozen bytes, then launching a 1GB guest?

> It is much easier to add ifdefs
> at the development stage then trying to figure out later what can be
> ifdeffed. If we will do:
> if (!(cnt = perf_guest_get_msrs_count())
> return;
>
> at the beginning of atomic_switch_perf_msrs() then compiler can
> eliminate dead code in case of !CONFIG_PERF_EVENTS since
> perf_guest_get_msrs_count() will become 0, but this will add two
> function calls on vmentry in CONFIG_PERF_EVENTS case.
>

Then move it to the beginning:

nr_msrs = perf_get_guest_msrs(&msr_buffer);
for (i = 0; i < nr_msrs; ++i)
add_atomic_switch_msr((*msr_buffer)[i], nr);

the compiler will kill the loop if nr_msrs is statically 0.

--
error compiling committee.c: too many arguments to function



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