On Tue, Oct 04, 2011 at 01:24:18PM +0200, Avi Kivity wrote: > 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. > Good idea. Just get rid of perf_guest_get_msrs_count(). -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
