From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: [PATCH] docs: Make note for the scheduler "cap" option warning about power management effects Date: Tue, 11 Jun 2013 13:31:38 +0100 Message-ID: <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: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org Cc: George Dunlap , Ian Jackson , Ian Campbell , Massimo Canonico List-Id: xen-devel@lists.xenproject.org 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. + =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