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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