From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH] docs: Make note for the scheduler "cap" option warning about power management effects Date: Wed, 12 Jun 2013 09:57:10 -0400 Message-ID: <20130612135710.GI2918@phenom.dumpdata.com> References: <1370953898-10278-1-git-send-email-george.dunlap@eu.citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1370953898-10278-1-git-send-email-george.dunlap@eu.citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: George Dunlap Cc: Ian Jackson , Massimo Canonico , Ian Campbell , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Tue, Jun 11, 2013 at 01:31:38PM +0100, George Dunlap wrote: > Suggested-by: Massimo Canonico > Signed-off-by: George Dunlap > CC: Ian Campbell > CC: Ian Jackson > CC: Massimo Canonico > --- > docs/man/xl.cfg.pod.5 | 13 +++++++++++++ > docs/man/xl.pod.1 | 13 +++++++++++++ > docs/man/xm.pod.1 | 13 +++++++++++++ > 3 files changed, 39 insertions(+) > > diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5 > index b7d64a6..069b73f 100644 > --- a/docs/man/xl.cfg.pod.5 > +++ b/docs/man/xl.cfg.pod.5 > @@ -153,6 +153,19 @@ The cap is expressed in percentage of one physical CPU: > The default, 0, means there is no upper cap. > Honoured by the credit and credit2 schedulers. > > +NB: Many systems have features that will scale down the computing > +power of a cpu that is not 100% utilized. This can be in the > +operating system, but can also sometimes be below the operating system > +in the BIOS. If you set a cap such that individual cores are running > +at less than 100%, this may have an impact on the performance of your > +workload over and above the impact of the cap. For example, if your > +processor runs at 2GHz, and you cap a vm at 50%, the power management > +system may also reduce the clock speed to 1GHz; the effect will be > +that your VM gets 25% of the available power (50% of 1GHz) rather than > +50% (50% of 2GHz). If you are not getting the performance you expect, > +look at performance and cpufreq options in your operating system and > +your BIOS. Or .. use 'cpufreq=xen:performance' ? That should set it to the highest P state. > + > =item B > > The normal EDF scheduling usage in nanoseconds. This means every period > diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1 > index 57c6a79..0e2fe65 100644 > --- a/docs/man/xl.pod.1 > +++ b/docs/man/xl.pod.1 > @@ -848,6 +848,19 @@ is expressed in percentage of one physical CPU: 100 is 1 physical CPU, > 50 is half a CPU, 400 is 4 CPUs, etc. The default, 0, means there is > no upper cap. > > +NB: Many systems have features that will scale down the computing > +power of a cpu that is not 100% utilized. This can be in the > +operating system, but can also sometimes be below the operating system > +in the BIOS. If you set a cap such that individual cores are running > +at less than 100%, this may have an impact on the performance of your > +workload over and above the impact of the cap. For example, if your > +processor runs at 2GHz, and you cap a vm at 50%, the power management > +system may also reduce the clock speed to 1GHz; the effect will be > +that your VM gets 25% of the available power (50% of 1GHz) rather than > +50% (50% of 2GHz). If you are not getting the performance you expect, > +look at performance and cpufreq options in your operating system and > +your BIOS. > + > =item B<-p CPUPOOL>, B<--cpupool=CPUPOOL> > > Restrict output to domains in the specified cpupool. > diff --git a/docs/man/xm.pod.1 b/docs/man/xm.pod.1 > index 7c4ef85..4d47388 100644 > --- a/docs/man/xm.pod.1 > +++ b/docs/man/xm.pod.1 > @@ -767,6 +767,19 @@ is expressed in percentage of one physical CPU: 100 is 1 physical CPU, > 50 is half a CPU, 400 is 4 CPUs, etc. The default, 0, means there is > no upper cap. > > +NB: Many systems have features that will scale down the computing > +power of a cpu that is not 100% utilized. This can be in the > +operating system, but can also sometimes be below the operating system > +in the BIOS. If you set a cap such that individual cores are running > +at less than 100%, this may have an impact on the performance of your > +workload over and above the impact of the cap. For example, if your > +processor runs at 2GHz, and you cap a vm at 50%, the power management > +system may also reduce the clock speed to 1GHz; the effect will be > +that your VM gets 25% of the available power (50% of 1GHz) rather than > +50% (50% of 2GHz). If you are not getting the performance you expect, > +look at performance and cpufreq options in your operating system and > +your BIOS. > + > =back > > =item B I I I I I > -- > 1.7.9.5 > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel >