From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46508) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f0wH5-0006xq-1F for qemu-devel@nongnu.org; Tue, 27 Mar 2018 17:37:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f0wH1-0006Ya-Sy for qemu-devel@nongnu.org; Tue, 27 Mar 2018 17:36:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46142) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f0wH1-0006Y7-NG for qemu-devel@nongnu.org; Tue, 27 Mar 2018 17:36:55 -0400 Date: Tue, 27 Mar 2018 18:36:46 -0300 From: Eduardo Habkost Message-ID: <20180327213646.GE5046@localhost.localdomain> References: <1521211002-4529-1-git-send-email-wanpengli@tencent.com> <20180327224058-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327224058-mutt-send-email-mst@kernel.org> Subject: Re: [Qemu-devel] [PATCH] i386/kvm: add support for KVM_CAP_X86_DISABLE_EXITS List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Wanpeng Li , qemu-devel@nongnu.org, kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= On Tue, Mar 27, 2018 at 10:42:56PM +0300, Michael S. Tsirkin wrote: > On Fri, Mar 16, 2018 at 07:36:42AM -0700, Wanpeng Li wrote: > > From: Wanpeng Li > > > > This patch adds support for KVM_CAP_X86_DISABLE_EXITS. Provides userspace with > > per-VM capability(KVM_CAP_X86_DISABLE_EXITS) to not intercept MWAIT/HLT/PAUSE > > in order that to improve latency in some workloads. > > [...] > > diff --git a/target/i386/kvm.c b/target/i386/kvm.c > > index d23fff1..95ed9eb 100644 > > --- a/target/i386/kvm.c > > +++ b/target/i386/kvm.c > > @@ -999,6 +999,18 @@ int kvm_arch_init_vcpu(CPUState *cs) > > } > > } > > > > + if (env->features[FEAT_KVM_HINTS] & KVM_HINTS_DEDICATED) { > > + int disable_exits = kvm_check_extension(cs->kvm_state, KVM_CAP_X86_DISABLE_EXITS); > > + if (disable_exits) { > > + disable_exits &= (KVM_X86_DISABLE_EXITS_MWAIT | > > + KVM_X86_DISABLE_EXITS_HLT | > > + KVM_X86_DISABLE_EXITS_PAUSE); > > + } > > + if (kvm_vm_enable_cap(cs->kvm_state, KVM_CAP_X86_DISABLE_EXITS, 0, disable_exits)) { > > + error_report("kvm: DISABLE EXITS not supported"); > > + } > > + } > > + > > qemu_add_vm_change_state_handler(cpu_update_state, env); > > > > c = cpuid_find_entry(&cpuid_data.cpuid, 1, 0); > > Why not a bit per capability? > I can see how someone might want to disable mwait exists > but not the rest of them. kvm-hint-dedicated=on should be used only if the physical CPU is dedicated to the VCPU task. Are there any advantages of getting vmexits for HLT and PAUSE if no other task is going to use the CPU? -- Eduardo