From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH RESEND v2] i386/kvm: add support for KVM_CAP_X86_DISABLE_EXITS Date: Wed, 16 May 2018 17:04:41 +0200 Message-ID: <2871c099-79fe-8432-12c9-637e743cc89c@redhat.com> References: <1523953455-28053-1-git-send-email-wanpengli@tencent.com> <20180417205913.GC29865@localhost.localdomain> <02887fa6-d7c8-bc39-6e65-3c3caec5b903@redhat.com> <20180419195610.GA29865@localhost.localdomain> <98f48c44-e55a-2bd2-0d41-5643f35bce68@redhat.com> <20180419215320.GC29865@localhost.localdomain> <20180512010007-mutt-send-email-mst@kernel.org> <20180516172121-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Wanpeng Li , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Eduardo Habkost , kvm@vger.kernel.org, qemu-devel@nongnu.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20180516172121-mutt-send-email-mst@kernel.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org On 16/05/2018 16:22, Michael S. Tsirkin wrote: >> kvm-hint-dedicated=on only sets the CPUID bit, which Linux for example >> uses that to disable pv spinlocks. "-realtime dedicated-cpus=on" only >> disables the vmexits. You can use the two independently. > > But when would you want to use the two independently? 1) For testing 2) When some of your QEMUs are too old to support kvm-hint-dedicated=on, you may still want to use -realtime dedicated-cpus=on to get better performance on the new one. Paolo From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50095) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fIxz1-0000Yq-Pg for qemu-devel@nongnu.org; Wed, 16 May 2018 11:04:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fIxyx-0004z5-RU for qemu-devel@nongnu.org; Wed, 16 May 2018 11:04:51 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:47936 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fIxyx-0004yu-Lu for qemu-devel@nongnu.org; Wed, 16 May 2018 11:04:47 -0400 References: <1523953455-28053-1-git-send-email-wanpengli@tencent.com> <20180417205913.GC29865@localhost.localdomain> <02887fa6-d7c8-bc39-6e65-3c3caec5b903@redhat.com> <20180419195610.GA29865@localhost.localdomain> <98f48c44-e55a-2bd2-0d41-5643f35bce68@redhat.com> <20180419215320.GC29865@localhost.localdomain> <20180512010007-mutt-send-email-mst@kernel.org> <20180516172121-mutt-send-email-mst@kernel.org> From: Paolo Bonzini Message-ID: <2871c099-79fe-8432-12c9-637e743cc89c@redhat.com> Date: Wed, 16 May 2018 17:04:41 +0200 MIME-Version: 1.0 In-Reply-To: <20180516172121-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH RESEND v2] 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: Eduardo Habkost , Wanpeng Li , qemu-devel@nongnu.org, kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= On 16/05/2018 16:22, Michael S. Tsirkin wrote: >> kvm-hint-dedicated=on only sets the CPUID bit, which Linux for example >> uses that to disable pv spinlocks. "-realtime dedicated-cpus=on" only >> disables the vmexits. You can use the two independently. > > But when would you want to use the two independently? 1) For testing 2) When some of your QEMUs are too old to support kvm-hint-dedicated=on, you may still want to use -realtime dedicated-cpus=on to get better performance on the new one. Paolo