From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 8/9] KVM, VMX: Add support for guest/host-only profiling Date: Tue, 04 Oct 2011 13:24:18 +0200 Message-ID: <4E8AECE2.7090206@redhat.com> References: <1317649795-18259-1-git-send-email-gleb@redhat.com> <1317649795-18259-9-git-send-email-gleb@redhat.com> <4E89CE09.1080808@redhat.com> <20111003153619.GA3225@redhat.com> <4E8AD1D3.9040402@redhat.com> <20111004095654.GE30105@redhat.com> <4E8AE9A0.2060706@redhat.com> <20111004111714.GG30105@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, joerg.roedel@amd.com, mingo@elte.hu, a.p.zijlstra@chello.nl To: Gleb Natapov Return-path: In-Reply-To: <20111004111714.GG30105@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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