From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45625) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VLayS-0007vA-Vj for qemu-devel@nongnu.org; Mon, 16 Sep 2013 11:44:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VLayK-0007wZ-I6 for qemu-devel@nongnu.org; Mon, 16 Sep 2013 11:44:28 -0400 Received: from nodalink.pck.nerim.net ([62.212.105.220]:36076 helo=paradis.irqsave.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VLayK-0007w6-7h for qemu-devel@nongnu.org; Mon, 16 Sep 2013 11:44:20 -0400 Date: Mon, 16 Sep 2013 17:46:04 +0200 From: =?iso-8859-1?Q?Beno=EEt?= Canet Message-ID: <20130916154603.GK5105@irqsave.net> References: <20130916121545.GH5105@irqsave.net> <8668D877-8B37-48E3-97B8-CE36DB884E54@suse.de> <20130916150544.GJ5105@irqsave.net> <20130916153239.GD906@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20130916153239.GD906@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] cpufreq and QEMU guests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: =?iso-8859-1?Q?Beno=EEt?= Canet , "peter.maydell@linaro.org" , "viresh.kumar@linaro.org" , Alexander Graf , "cpufreq@vger.kernel.org" , "qemu-devel@nongnu.org" , "rjw@sisk.pl" , "pbonzini@redhat.com" Le Monday 16 Sep 2013 =E0 18:32:39 (+0300), Gleb Natapov a =E9crit : > On Mon, Sep 16, 2013 at 05:05:45PM +0200, Beno=EEt Canet wrote: > > Le Monday 16 Sep 2013 =E0 09:39:10 (-0500), Alexander Graf a =E9crit = : > > >=20 > > >=20 > > > Am 16.09.2013 um 07:15 schrieb Beno=EEt Canet : > > >=20 > > > >=20 > > > > Hello, > > > >=20 > > > > I know a cloud provider worried about the fact that the /proc/cpu= info of his > > > > guests give a bogus frequency to his customer. > > > >=20 > > > > QEMU and the guests kernel currently have no way to reflect the h= ost frequency > > > > changes to the guests. > > > >=20 > > > > The customer compute intensive application then read this informa= tion and take > > > > wrong decisions. > > >=20 > > > Why do they care about the frequency? Is it for scheduling workload= s? The only other case I can think of would be the TSC and that should be= fixed frequency these days. > > >=20 > > > If it's scheduling, you could maybe expose the unavailable compute = time as steal time to the guest. Exposibg frequency in a virtual environm= ent feels backwards. > >=20 > > The final customer have a compute intensive workload. > > At startup the code retrieve the cpu cache topology, the cpu model, a= nd various > > informations including the guest cpu frequency before starting the co= mpute job. > > The QEMU instance typicaly use -cpu host. > >=20 > > The code inspects the cpu frequency has seen by the guests to choose = the number > > of vms to instanciate to compute the given task. > I am not sure I understand. They look at guest cpu frequency to estimat= e > guest's performance? Yes they take guest cpu count, model and frequency to estimate the perfor= mance of the guest. Next they cluster enough guests to be able to compute the job in a given = time by using this estimate. Best regards Beno=EEt >=20 > > They even destroy and recreate some vms that would be underperforming= to > > mitigate the high inter vm communication costs. > >=20 > > Do you think the steal time trick would work for this ? > >=20 >=20 > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe cpufreq" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html