From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH RESEND v2] i386/kvm: add support for KVM_CAP_X86_DISABLE_EXITS Date: Wed, 16 May 2018 17:22:10 +0300 Message-ID: <20180516172121-mutt-send-email-mst@kernel.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Wanpeng Li , Radim =?utf-8?B?S3LEjW3DocWZ?= , Eduardo Habkost , kvm@vger.kernel.org, qemu-devel@nongnu.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: 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 Wed, May 16, 2018 at 02:44:24PM +0200, Paolo Bonzini wrote: > On 12/05/2018 00:12, Michael S. Tsirkin wrote: > >> Maybe it's a better idea than overloading an option that is only > >> expected to control a CPUID bit. > > Well -realtime would be a bit confusing in that it enables mlock by > > default. > > Currently, the only suboption of "-realtime" is mlock, which means that > the only three valid uses of it are > > -realtime mlock=on > -realtime mlock=off > -realtime '' > > We can change the default, I think. Only the third would change > meaning, and it's a slightly crazy way to use the option. > > > From pure API point of view, hint-dedicated looks good since > > it seems to say "optimize for a dedicated host CPU" and > > it's a hint in that guests keep working if you violate this > > slightly once in a while. > > > > But I agree there's a problem: right now "kvm-" means "KVM PV" > > as opposed to e.g. HV enlightened gusts. > > So if you enable hyperv and also want to disable halt existing, > > what then? What should kvm-hint-dedicated=on do? > > 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? > Thanks, > > Paolo > > > So how about a new hint-dedicated=on cpu flag? We can have that set > > kvm-hint-dedicated if kvm PV is enabled. > >