From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH RFC V4 5/5] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock Date: Tue, 17 Jan 2012 13:53:03 -0200 Message-ID: <20120117155303.GA28904@amt.cnet> References: <20120116094020.GA6019@linux.vnet.ibm.com> <4F13F883.5090002@redhat.com> <20120116141117.GB6019@linux.vnet.ibm.com> <20120117091413.GM2167@redhat.com> <20120117122650.GC30757@linux.vnet.ibm.com> <20120117125126.GQ2167@redhat.com> <20120117131103.GD30398@linux.vnet.ibm.com> <20120117132051.GR2167@redhat.com> <20120117142818.GE30398@linux.vnet.ibm.com> <20120117153233.GA7911@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jeremy Fitzhardinge , Raghavendra K T , KVM , linux-doc@vger.kernel.org, Peter Zijlstra , Jan Kiszka , Srivatsa Vaddagiri , Paul Mackerras , "H. Peter Anvin" , Stefano Stabellini , Xen , Dave Jiang , Glauber Costa , X86 , Ingo Molnar , Avi Kivity , Rik van Riel , Konrad Rzeszutek Wilk , Sasha Levin , Sedat Dilek , Thomas Gleixner , Virtualization , Greg Kroah-Hartman , LKML < To: Gleb Natapov , Anthony Liguori Return-path: Content-Disposition: inline In-Reply-To: <20120117153233.GA7911@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: kvm.vger.kernel.org On Tue, Jan 17, 2012 at 05:32:33PM +0200, Gleb Natapov wrote: > On Tue, Jan 17, 2012 at 07:58:18PM +0530, Srivatsa Vaddagiri wrote: > > * Gleb Natapov [2012-01-17 15:20:51]: > > > > > > Having the hypercall makes the intent of vcpu (to sleep on a kick) clear to > > > > hypervisor vs assuming that because of a trapped HLT instruction (which > > > > will anyway won't work when yield_on_hlt=0). > > > > > > > The purpose of yield_on_hlt=0 is to allow VCPU to occupy CPU for the > > > entire time slice no mater what. I do not think disabling yield on HLT > > > is even make sense in CPU oversubscribe scenario. > > > > Yes, so is there any real use for yield_on_hlt=0? I believe Anthony > > initially added it as a way to implement CPU bandwidth capping for VMs, > > which would ensure that busy VMs don't eat into cycles meant for a idle > > VM. Now that we have proper support in scheduler for CPU bandwidth capping, is > > there any real world use for yield_on_hlt=0? If not, deprecate it? > > > I was against adding it in the first place, so if IBM no longer needs it > I am for removing it ASAP. +1. Anthony? From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH RFC V4 5/5] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock Date: Tue, 17 Jan 2012 13:53:03 -0200 Message-ID: <20120117155303.GA28904@amt.cnet> References: <20120116094020.GA6019@linux.vnet.ibm.com> <4F13F883.5090002@redhat.com> <20120116141117.GB6019@linux.vnet.ibm.com> <20120117091413.GM2167@redhat.com> <20120117122650.GC30757@linux.vnet.ibm.com> <20120117125126.GQ2167@redhat.com> <20120117131103.GD30398@linux.vnet.ibm.com> <20120117132051.GR2167@redhat.com> <20120117142818.GE30398@linux.vnet.ibm.com> <20120117153233.GA7911@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20120117153233.GA7911@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Gleb Natapov , Anthony Liguori Cc: Jeremy Fitzhardinge , Raghavendra K T , KVM , linux-doc@vger.kernel.org, Peter Zijlstra , Jan Kiszka , Srivatsa Vaddagiri , Paul Mackerras , "H. Peter Anvin" , Stefano Stabellini , Xen , Dave Jiang , Glauber Costa , X86 , Ingo Molnar , Avi Kivity , Rik van Riel , Konrad Rzeszutek Wilk , Sasha Levin , Sedat Dilek , Thomas Gleixner , Virtualization , Greg Kroah-Hartman List-Id: virtualization@lists.linuxfoundation.org On Tue, Jan 17, 2012 at 05:32:33PM +0200, Gleb Natapov wrote: > On Tue, Jan 17, 2012 at 07:58:18PM +0530, Srivatsa Vaddagiri wrote: > > * Gleb Natapov [2012-01-17 15:20:51]: > > > > > > Having the hypercall makes the intent of vcpu (to sleep on a kick) clear to > > > > hypervisor vs assuming that because of a trapped HLT instruction (which > > > > will anyway won't work when yield_on_hlt=0). > > > > > > > The purpose of yield_on_hlt=0 is to allow VCPU to occupy CPU for the > > > entire time slice no mater what. I do not think disabling yield on HLT > > > is even make sense in CPU oversubscribe scenario. > > > > Yes, so is there any real use for yield_on_hlt=0? I believe Anthony > > initially added it as a way to implement CPU bandwidth capping for VMs, > > which would ensure that busy VMs don't eat into cycles meant for a idle > > VM. Now that we have proper support in scheduler for CPU bandwidth capping, is > > there any real world use for yield_on_hlt=0? If not, deprecate it? > > > I was against adding it in the first place, so if IBM no longer needs it > I am for removing it ASAP. +1. Anthony?