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Date: Thu, 30 Nov 2006 03:19:33 -0800 From: Andrew Morton <akpm@...l.org> To: Ingo Molnar <mingo@...e.hu> Cc: Gautham R Shenoy <ego@...ibm.com>, linux-kernel@...r.kernel.org, torvalds@...l.org, davej@...hat.com, dipankar@...ibm.com, vatsa@...ibm.com Subject: Re: CPUFREQ-CPUHOTPLUG: Possible circular locking dependency On Thu, 30 Nov 2006 12:03:15 +0100 Ingo Molnar <mingo@...e.hu> wrote: > > * Gautham R Shenoy <ego@...ibm.com> 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." > > ? How does this differ from stop_machine_run(), which hot-unplug presently uses? > 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. You said "the hotplug lock". That is the problem. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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