From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759395AbYE0SZk (ORCPT ); Tue, 27 May 2008 14:25:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759127AbYE0SYp (ORCPT ); Tue, 27 May 2008 14:24:45 -0400 Received: from e28smtp03.in.ibm.com ([59.145.155.3]:47710 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758211AbYE0SYo (ORCPT ); Tue, 27 May 2008 14:24:44 -0400 Date: Tue, 27 May 2008 23:56:04 +0530 From: Vaidyanathan Srinivasan To: Arjan van de Ven Cc: Linux Kernel , venkatesh.pallipadi@intel.com, suresh.b.siddha@intel.com, Michael Neuling , Balbir Singh , "Amit K. Arora" Subject: Re: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86 Message-ID: <20080527182604.GK5181@dirshya.in.ibm.com> Reply-To: svaidy@linux.vnet.ibm.com Mail-Followup-To: Arjan van de Ven , Linux Kernel , venkatesh.pallipadi@intel.com, suresh.b.siddha@intel.com, Michael Neuling , Balbir Singh , "Amit K. Arora" References: <20080526142513.24680.97164.stgit@drishya.in.ibm.com> <20080526085000.33787eac@infradead.org> <20080527140440.GD5181@dirshya.in.ibm.com> <20080527094035.67ccda32@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20080527094035.67ccda32@infradead.org> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Arjan van de Ven [2008-05-27 09:40:35]: > On Tue, 27 May 2008 19:34:40 +0530 > Vaidyanathan Srinivasan wrote: > > > > What we are proposing is a scaled time value that is scaled to the > > current CPU capacity. If the scaled utilisation is 50% when the CPU > > is at 100% capacity, it is expected to remain at 50% even if the CPU's > > capacity is dropped to 50%, while the traditional utilisation value > > will be 100%. > > When you use the word "capacity" I cringe ;( > > > > > The problem in the above two cases is that we had assumed that the > > maximum CPU capacity is 100% at normal capacity (without IDA). > > > > If the CPU is at half the maximum frequency, then scaled stats should > > show 50%. > > see frequency != capacity. > It's about more than frequency. It's about how much cache you have > available too. If you run single threaded on a dual core cpu, you have > 100% of the cache, but the cpu is 50% idle. But that doesn't mean that > when you double the load, you actually get 2x the performance. So > you're not at 50% of capacity! You are right.... I kind of interchangeably used frequency and capacity assuming capacity is linearly proportional to frequency! In reality, I agree that capacity is not linearly proportional to frequency and it is dependent on cache usage etc. The differences apart, I am sure I have conveyed the relationship between scaled stats and CPU frequency. I used the term 'capacity' to generalise CPU performance, but I guess it may lead to a different discussion. I will stick to frequency. :) --Vaidy > > The point I am trying to make is whether scaling should be done > > relative to CPUs designed maximum capacity or maximum capacity under > > current constraints is to be discussed. > > now you're back at "capacity".. we were at frequency before ;( > > > > > > Case A: > > ------ > > > > Scaled stats is stats relative to maximum designed capacity including > > IDA > > you don't know what that is though. >