lkml.org 
[lkml]   [2011]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 8/9] KVM, VMX: Add support for guest/host-only profiling
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



\
 
 \ /
  Last update: 2011-10-04 13:13    [from the cache]
©2003-2011 Jasper Spaans