On Wednesday, January 18, 2012, mark gross wrote: > On Mon, Jan 16, 2012 at 10:38:57PM +0100, Rafael J. Wysocki wrote: > > Hi, > > > > On Monday, January 16, 2012, Antti P Miettinen wrote: > > > [did not reach linux-pm as I sent to wrong address, sorry for > > > duplicates] > > > > > > The inspiration for this patch series is the N9 CPU frequency boost > > > upon input events: > > > > > > http://www.spinics.net/lists/cpufreq/msg00667.html > > > > > > and the related changes in git://codeaurora.org/kernel/msm.git tree. > > > Those patches modify the ondemand cpufreq governor. This patch series > > > adds minimum and maximum CPU frequency as PM QoS parameters and > > > modifies the cpufreq core to enforce the PM QoS limits. > > > > If that hasn't been clear enough so far, I'm still not convinced that using > > PM QoS for that is a good idea. > > > > First off, frequency as a unit of throughput is questionable to say the least, > > because it isn't portable from one system to another. Moreover, even on a > > given system it isn't particularly clear what the exact correspondence > > between frequency and throughput actually is. > > You are right. The notion of throughput of a CPU is really hard to > quantify. Perhaps not using the term "throughput" would help? Yes, it would. > The base issue I see, the Intel platform, is needing is that sometimes > we need to block the lowest P-states that the ondemand governor goes for > because those P-states result in media / graphics workloads dropping > frames. However; GPU intensive workloads do not stress the CPU so the > ondemand governor goes for the low p-state. > > I could use some way of constraining the PM-throttling of the > cpu-freq that can be hit from kernel or user mode. So the graphics > driver can dynamically adjust the constraint request on the cpufreq > subsystem. > > It is problematic that any driver requesting a given frequency request > is not portable across ISA's or even processor families in the same ISA. > But, maybe such a driver should use a module parameter to work around > this lack of portability? Well, it seems to me that we're trying to add a backdoor to the (apparently inadequate) governors here. Arguably, the governors should be able to make the right decisions on the basis of the information they receive through their own interfaces. > > Second, it's not particularly clear what the meaning of the "min" frequency > > is supposed to be in terms of throughput. > > It should mean "please cpufreq do not put the cpu into a state where its > clock runs slower than min". I don't think we should talk about it as > throughput because thats not what the cpufreq controls. Perhaps we need a new cpufreq governor that would take use PM QoS internally to store requests from different sources, but that would work on a per-CPU basis (not globally) and would provide a new interface for user space? Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
