On Thu, Nov 30, 2006 at 12:03:15PM +0100, Ingo Molnar wrote: > > * Gautham R Shenoy <[EMAIL PROTECTED]> wrote: > > > a) cpufreq maintain's it's own cpumask in the variable > > policy->affected_cpus and says : If a frequency change is issued to > > any one of the cpu's in the affected_cpus mask, you change frequency > > on all cpus in the mask. So this needs to be consistent with > > cpu_online map and hence cpu hotplug aware. Furthermore, we don't want > > cpus in this mask to go down when we are trying to change frequencies > > on them. The function which drives the frequency change in > > cpufreq-core is cpufreq_driver_target and it needs cpu-hotplug > > protection. > > couldnt this complexity be radically simplified by having new kernel > infrastructure that does something like: > > " 'gather' all CPUs mentioned in <mask> via scheduling a separate > helper-kthread on every CPU that <mask> specifies, disable all > interrupts, and execute function <fn> once all CPUs have been > 'gathered' - and release all CPUs once <fn> has executed on each of > them." > > ?
This is what is currently being done by cpufreq: a) get_some_cpu_hotplug_protection() [use either some global mechanism or a persubsystem mutex] b) actual_freq_change_driver_function(mask) /* You can check out cpufreq_p4_target() in * arch/i386/kernel/cpu/cpufreq/p4-clockmod.c */ { for_each_cpu_mask(i, mask) { cpumask_t this_cpu = cpumask_of_cpu(i); set_cpus_allowed(current, this_cpu); function_to_change_frequency(); } } c) release_whatever_cpu_hotplug_protection() > > This would be done totally serialized and while holding the hotplug > lock, so no CPU could go away or arrive while this operation is going > on. > Isn't the above same as what you are suggesting? Or have I missed out anything? > Ingo regards gautham. -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" - 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/