From mboxrd@z Thu Jan 1 00:00:00 1970 From: arjan@linux.intel.com (Arjan van de Ven) Date: Fri, 26 Apr 2013 08:46:21 -0700 Subject: [RFC PATCH v4 00/14] sched: packing small tasks In-Reply-To: References: <1366910611-20048-1-git-send-email-vincent.guittot@linaro.org> <517A969B.5040606@linux.intel.com> Message-ID: <517AA14D.7060202@linux.intel.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org >> >> >> so I got to ask the hard question; what percentage of system level (not just >> cpu level) >> power consumption gain can you measure (pick your favorite workload)... >> > > I haven't system level figures for my patches but only for the cpu > subsystem. If we use the MP3 results in the back of my mail, they show > an improvement of 37 % (113/178) for the CPU subsystem of the > platform. If we assume that the CPU subsystem contributes 25% of an > embedded system power consumption (this can vary across platform > depending of the use of HW accelerator but it should be a almost fair > percentage), the patch can impact the power consumption on up to 9%. > sadly the math tends to not work quite that easy; memory takes significantly more power when the system is not idle than when it is idle for example. [*] so while reducing cpu power by making it run a bit longer (at lower frequency or slower core or whatever) is a pure win if you only look at the cpu, but it may (or may not) be a loss when looking at a whole system level. I've learned the hard way that you cannot just look at the cpu numbers; you must look at the whole-system power when playing with such tradeoffs. That does not mean that your patch is not useful; it very well can be, but without having looked at whole-system power that's a very dangerous conclusion to make. So.. if you get a chance, I'd love to see data on a whole-system level... even for just one workload and one system (playing mp3 sounds like a quite reasonable workload for such things indeed) [*] I assume that on your ARM systems, memory goes into self refresh during system idle just as it does on x86