From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42333) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f9HUd-0002SL-Ra for qemu-devel@nongnu.org; Thu, 19 Apr 2018 17:53:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f9HUa-00038Z-Nn for qemu-devel@nongnu.org; Thu, 19 Apr 2018 17:53:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38940) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f9HUa-00037b-H7 for qemu-devel@nongnu.org; Thu, 19 Apr 2018 17:53:24 -0400 Date: Thu, 19 Apr 2018 18:53:20 -0300 From: Eduardo Habkost Message-ID: <20180419215320.GC29865@localhost.localdomain> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <98f48c44-e55a-2bd2-0d41-5643f35bce68@redhat.com> 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: Paolo Bonzini Cc: Wanpeng Li , qemu-devel@nongnu.org, kvm@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= On Thu, Apr 19, 2018 at 11:32:16PM +0200, Paolo Bonzini wrote: > On 19/04/2018 21:56, Eduardo Habkost wrote: > > On Thu, Apr 19, 2018 at 05:48:57PM +0200, Paolo Bonzini wrote: > >> On 17/04/2018 22:59, Eduardo Habkost wrote: > >>>> + if (disable_exits) { > >>>> + disable_exits &= (KVM_X86_DISABLE_EXITS_MWAIT | > >>>> + KVM_X86_DISABLE_EXITS_HLT | > >>>> + KVM_X86_DISABLE_EXITS_PAUSE); > >>>> + if (env->user_features[FEAT_KVM] & KVM_PV_UNHALT) { > >>>> + disable_exits &= ~KVM_X86_DISABLE_EXITS_HLT; > >>>> + } > >>> > >>> In the future, if we decide to enable kvm-pv-unhalt by default, > >>> should "-cpu ...,kvm-hint-dedicated=on" disable kvm-pv-unhalt > >>> automatically, or should we require an explicit > >>> "kvm-hint-dedicated=on,kvm-pv-unhalt=off" option? > >> > >> It should be automatic. > >> > >>> For today's defaults, this patch solves the problem, only one > >>> thing is missing before I give my R-b: we need to clearly > >>> document what exactly are the consequences and requirements of > >>> setting kvm-hint-dedicated=on (I'm not sure if the best place for > >>> this is qemu-options.hx, x86_cpu_list(), or somewhere else). > >> > >> I don't think we have a good place for this kind of documentation, > >> unfortunately. Right now it is mentioned in > >> Documentation/virtual/kvm/cpuid.txt. > > > > With this patch, the QEMU option will do more than just setting > > the CPUID bit, that's why I miss more detailed documentation on > > the QEMU side. But I agree we have no obvious place for that > > documentation. > > > > In the worst case we can just add a code comment on top of > > feature_word_info[FEAT_KVM_HINTS].feat_names warning that > > kvm-hint-dedicated won't just enable the flag on CPUID and has > > other side-effects. > > Maybe we should use "-realtime dedicated=on" instead of, or in addition > to kvm-hint-dedicated=on? Maybe it's a better idea than overloading an option that is only expected to control a CPUID bit. -- Eduardo