>-----Original Message----- >From: Darrick J. Wong [mailto:[EMAIL PROTECTED] >Sent: Friday, June 01, 2007 11:44 AM >To: Pallipadi, Venkatesh >Cc: linux-kernel@vger.kernel.org >Subject: Re: Dependent CPU core speed reporting not updated >with CPUFREQ_SHARED_TYPE_HW? > >On Thu, Mar 29, 2007 at 06:06:22PM -0700, Pallipadi, Venkatesh wrote: >> thought of >> making affected CPUs show the dependency in case of hw coord, but >> retaining the percpu >> control. But, it seemed complicated change for something that is >> cosmetic. > >Actually, it's not so cosmetic any more. Our newest servers have a >power meter that measures power consumption, and I'm writing a program >to measure the power cost of various cpufreq transitions in order to >enforce a power cap. Due to the under-reporting in affected_cpus, the >app thinks that (taking your example above) CPUs 0 and 2 can be >controlled independently. Thus, a p-state transition of (x, x) -> >(x, x-1) yields no energy saving at all, while (x, x-1) -> (x-1, x-1) >does. My program considers the effects of a single CPU's transition >independently of which CPU it is and without considering what >frequencies the other CPUs are operating at, which means that it will >conclude that the cost of increasing speed (or the reward for >decreasing >it) is half of what it is ... sort of. It's mildly broken as a result, >though amusingly enough it still seems to work ok. I suspect that it >might flail around trying to hit a cap a bit more than it would if >affected_cpus were more accurate.
Hmmm. How about having a new cpufreq_sysfs entry to say these CPUs are frequency dependent in hardware. affected_cpus today has a single cpufreq directory for all affected_cpus and we coordinate all CPUs in software. To change freq, we will have to move among all affected_cpus and write an MSR. Hardware coordination basically tells us that kernel can control frequency percpu, but underneath hardware will pick highest requested freq among a group of CPUs. Instaed of handling this case as the existing software coordination case above, we can add a new entry in cpufreq /sysfs denoting hardware coordinated CPU group. Though it will be confusing with too many interfaces, I feel this is the right way to go about here. Comments? Thoughts? Thanks, Venki - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/