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Date: Thu, 01 Mar 2012 17:37:37 -0800 From: Suresh Siddha <suresh.b.siddha@...el.com> To: Venki Pallipadi <venki@...gle.com> Cc: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Aaron Durbin <adurbin@...gle.com>, Paul Turner <pjt@...gle.com>, Yong Zhang <yong.zhang0@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] Extend mwait idle to optimize away CAL and RES interrupts to an idle CPU -v1 On Thu, 2012-03-01 at 17:35 -0800, Venki Pallipadi wrote: > On Thu, Mar 1, 2012 at 5:28 PM, Suresh Siddha <suresh.b.siddha@...el.com> wrote: > > On Thu, 2012-03-01 at 16:33 -0800, Venki Pallipadi wrote: > >> > > >> > fork_idle() should also make sure it does not schedule the child > >> > thread: thus we'd also be able to further simplify smpboot.c and > >> > get rid of all that extremely ugly 'struct create_idle' > >> > gymnastics in smpboot.c. > >> > >> But not this. I am not sure where fork_idle results in resched of the child. > >> As I saw it, fork_idle calls init_idle and that sets the affinity of > >> idle_task to target CPU. So, reschedule should not be a problem. What > >> am I missing here? > > > > I think Ingo is referring to the fact that we can't use kthread_create() > > here and hence we were relying on fork_idle(). > > > >> Also, I tried this silly test patch (Cut and paste... Sorry) and it > >> seemed to work fine both with and without CPU hotplug. > >> > > > > I don't think we can do this today, as we need to make sure we have the > > correct current context. With dynamic cpu hotplug, current context can > > be any process and hence we were depending on the schedule_work() > > context. > > > > schedule_work() is only done at boot time. In case of dynamic cpu > hotplug, we skip the whole fork_idle as we already have the task > struct and just do init_idle(). > What happens if we boot with "maxcpus=" and later online the remaining cpu's? same issue with the physical cpu-online case too right? thanks, suresh -- 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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