Messages in this thread | | | Date | Tue, 04 Oct 2011 13:24:18 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH 8/9] KVM, VMX: Add support for guest/host-only profiling |
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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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