From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH 2 of 2] vpmu: Add a vpmu cpuid function Date: Fri, 20 Jan 2012 10:54:44 +0000 Message-ID: References: <8568566.QXZZClQmLn@amur> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <8568566.QXZZClQmLn@amur> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Dietmar Hahn Cc: Wei Wang , "xen-devel@lists.xensource.com" , Haitao Shan List-Id: xen-devel@lists.xenproject.org On 20/01/2012 10:49, "Dietmar Hahn" wrote: >> Our CPUID configuration is done per-domain, and from >> tools/libxc/xc_cpuid_x86.c. CPUID adjustments implemented within the >> hypervisor are generally not acceptable without very good reason. > > Then a way is needed to have access to the opt_vpmu_enabled variable within > the > hypervisor from the tools to decide the enabling of the flag (is there such a > way?) or the mechanism with the boot variable must be changed. > The opt_vpmu_enabled boot variable was introduced because of a PMU problem in > the Nehalem cpus leading sometimes to hypervisor crashes. But with the done > quirk we never had a crash anymore. > So maybe we can always switch on the vpmu stuff in the hypervisor and add a > flag in the domain configuration when somebody wants to do some performance > tests? Yes! It's obviously an option of fairly narrow interest. If someone tries to enable the per-domain option on a CPU which has problems, you can fail the domain creation, or print a warning in the hypervisor log, or whatever. Any sensible option in that respect is fine by me! -- Keir