On Tue, 2011-10-11 at 12:46 +0530, Amit Kucheria wrote: > Adding Peter to the discussion..
Right, CCing the folks who actually wrote the code you're asking questions about always helps ;-) > On Thu, Oct 6, 2011 at 5:06 PM, Vincent Guittot > <vincent.guit...@linaro.org> wrote: > > I work to link the cpu_power of ARM cores to their frequency by using > > arch_scale_freq_power. Why and how? In particular note that if you're using something like the on-demand cpufreq governor this isn't going to work. > It's explained in the kernel that cpu_power is > > used to distribute load on cpus and a cpu with more cpu_power will > > pick up more load. The default value is SCHED_POWER_SCALE and I > > increase the value if I want a cpu to have more load than another one. > > Is there an advised range for cpu_power value as well as some time > > scale constraints for updating the cpu_power value ? Basically 1024 is the unit and denotes the capacity of a full core at 'normal' speed. Typically cpufreq would down-clock a core and thus you'd end up with a smaller number (linearly proportional to the freq ratio etc. although if you want to go really fancy you could determine the actual throughput/freq curves). Things like x86 turbo mode would result in a >1024 value. Things like SMT would typically result in <1024 and the SMT sum over the core >1024 (if you're lucky). > > I'm also wondering why this scheduler feature is currently disable by > > default ? Because the only implementation in existence (x86) is broken and I haven't gotten around to fixing it. Arguable we should disable that for the time being, see below. > In discussions with Vincent regarding this, I've wondered whether > cpu_power wouldn't be better renamed to cpu_capacity since that is > what it really seems to describe. Possibly, but its been cpu_power for ages and we use capacity to describe something else. --- arch/x86/kernel/cpu/sched.c | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-) diff --git a/arch/x86/kernel/cpu/sched.c b/arch/x86/kernel/cpu/sched.c index a640ae5..90ae68c 100644 --- a/arch/x86/kernel/cpu/sched.c +++ b/arch/x86/kernel/cpu/sched.c @@ -6,7 +6,14 @@ #include <asm/cpufeature.h> #include <asm/processor.h> -#ifdef CONFIG_SMP +#if 0 /* def CONFIG_SMP */ + +/* + * Currently broken, we need to filter out idle time because the aperf/mperf + * ratio measures actual throughput, not capacity. This means that if a logical + * cpu idles it will report less capacity and receive less work, which isn't + * what we want. + */ static DEFINE_PER_CPU(struct aperfmperf, old_perf_sched); _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
