On 10/04/2011 11:56 AM, Gleb Natapov wrote:
On Tue, Oct 04, 2011 at 11:28:51AM +0200, Avi Kivity wrote:
> On 10/03/2011 05:36 PM, Gleb Natapov wrote:
> >On Mon, Oct 03, 2011 at 05:00:25PM +0200, Avi Kivity wrote:
> >> On 10/03/2011 03:49 PM, Gleb Natapov wrote:
> >> >Support guest/host-only profiling by switch perf msrs on
> >> >a guest entry if needed.
> >> >
> >> >@@ -6052,6 +6056,26 @@ static void vmx_cancel_injection(struct kvm_vcpu *vcpu)
> >> > vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);
> >> > }
> >> >
> >> >+static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
> >> >+{
> >> >+#ifdef CONFIG_PERF_EVENTS
> >>
> >> No need for #ifdef (if you also define perf_guest_get_msrs() when
> >> !CONFIG_PERF_EVENTS).
> >>
> >Yes, but will compiler be smart enough to remove the code of the
> >function completely? It will have to figure that vmx->perf_msrs_cnt is
> >always 0 somehow.
>
> It won't, but do we care?
>
Dead code, that likely to be inlined, on a hot path.
I mean, CONFIG_KVM && !CONFIG_PERF_EVENTS is an unlikely combination.
If you're using kvm, you usually want PERF_EVENTS.
> >VMWRITE happens only when number of autoloaded MSRs changes (which is
> >rare), not on each call to add_atomic_switch_msr(). I thought about
> >optimizing this write too by doing
> >vmcs_write32(VM_(ENTRY|EXIT)_MSR_LOAD_COUNT, m->nr) only once by
> >checking that m->nr changed during vmentry. Can be done later.
>
> For EFER and PERF_CTRL, it's done unconditionally, no?
For those yes. We do not cache their value currently. Can be added, but
this is independent optimization.
Sure. I note that on most cpus only these will ever be used.
--
error compiling committee.c: too many arguments to function
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