From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: Re: Overall picture of cpufreq.. Date: Mon, 14 Jan 2008 08:08:50 +0100 Message-ID: <478B0A82.6050503@wpkg.org> References: <9f79f7f50801111415w354dc91fwfeec98b16a00fb74@mail.gmail.com> <1200264884.4157.16.camel@queen> <9f79f7f50801131812x6a68c202tb4c25fa2116b32e4@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9f79f7f50801131812x6a68c202tb4c25fa2116b32e4@mail.gmail.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: cpufreq-bounces@lists.linux.org.uk Errors-To: cpufreq-bounces+glkc-cpufreq=m.gmane.org+glkc-cpufreq=m.gmane.org@lists.linux.org.uk To: Saru Addep Cc: cpufreq@lists.linux.org.uk, Martin.Leisner@xerox.com Saru Addep schrieb: > Hi Thomas, > > So that means if we have an ondemand governor properly instrumented, there > is no need to have userspace governor. In the case of ondemand governor, the > only work that will be left to userspace would be to set the min, and max > freq. The complete intelligence of DVFS algoritm is present inside the > ondemand governor. Is my understanding correct. It looks to me that ondemand governor doesn't have "the complete intelligence". For example, it doesn't detect CPU load coming from some kernel tasks, like kcryptd: reads/writes from a device crypted with dm-crypt will be very slow if one uses the ondemand governor, as CPU speed will always be set to the lowest possible (so there is not enough power to crypt/decrypt data). Ironically, this is the only case when starting bzip2 will speed up your disk access... Or, use a userspace governor. See also http://bugzilla.kernel.org/show_bug.cgi?id=9729 -- Tomasz Chmielewski http://wpkg.org