From: Avi Kivity <avi@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
joerg.roedel@amd.com, mingo@elte.hu, a.p.zijlstra@chello.nl
Subject: Re: [PATCH 8/9] KVM, VMX: Add support for guest/host-only profiling
Date: Tue, 04 Oct 2011 13:10:24 +0200 [thread overview]
Message-ID: <4E8AE9A0.2060706@redhat.com> (raw)
In-Reply-To: <20111004095654.GE30105@redhat.com>
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
next prev parent reply other threads:[~2011-10-04 11:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-03 13:49 [PATCH 0/9] perf support for x86 guest/host-only bits Gleb Natapov
2011-10-03 13:49 ` [PATCH 1/9] perf, core: Introduce attrs to count in either host or guest mode Gleb Natapov
2011-10-03 13:49 ` [PATCH 2/9] perf, amd: Use GO/HO bits in perf-ctr Gleb Natapov
2011-10-03 13:49 ` [PATCH 3/9] perf, tools: Add support for guest/host-only profiling Gleb Natapov
2011-10-03 13:49 ` [PATCH 4/9] perf, tools: Fix copy&paste error in perf-kvm option description Gleb Natapov
2011-10-03 13:49 ` [PATCH 5/9] perf, tools: Do guest-only counting in perf-kvm by default Gleb Natapov
2011-10-03 13:49 ` [PATCH 6/9] perf, intel: Use GO/HO bits in perf-ctr Gleb Natapov
2011-10-03 15:06 ` Avi Kivity
2011-10-03 15:41 ` Gleb Natapov
2011-10-04 9:21 ` Avi Kivity
2011-10-03 13:49 ` [PATCH 7/9] KVM, VMX: add support for switching of PERF_GLOBAL_CTRL Gleb Natapov
2011-10-04 9:32 ` Avi Kivity
2011-10-04 9:57 ` Gleb Natapov
2011-10-03 13:49 ` [PATCH 8/9] KVM, VMX: Add support for guest/host-only profiling Gleb Natapov
2011-10-03 15:00 ` Avi Kivity
2011-10-03 15:36 ` Gleb Natapov
2011-10-04 9:28 ` Avi Kivity
2011-10-04 9:56 ` Gleb Natapov
2011-10-04 11:10 ` Avi Kivity [this message]
2011-10-04 11:17 ` Gleb Natapov
2011-10-04 11:24 ` Avi Kivity
2011-10-04 12:12 ` Gleb Natapov
2011-10-03 13:49 ` [PATCH 9/9] KVM, VMX: Check for automatic switch msr table overflow Gleb Natapov
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