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Date: Thu, 1 Mar 2012 17:35:37 -0800 From: Venki Pallipadi <venki@...gle.com> To: Suresh Siddha <suresh.b.siddha@...el.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, 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(). > thanks, > suresh > >> Thanks, >> Venki >> >> --- >> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c >> index 66d250c..36b80ef 100644 >> --- a/arch/x86/kernel/smpboot.c >> +++ b/arch/x86/kernel/smpboot.c >> @@ -686,7 +686,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu) >> .done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done), >> }; >> >> - INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle); >> + // INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle); >> >> alternatives_smp_switch(1); >> >> @@ -703,12 +703,13 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu) >> goto do_rest; >> } >> >> - schedule_work(&c_idle.work); >> - wait_for_completion(&c_idle.done); >> + // schedule_work(&c_idle.work); >> + // wait_for_completion(&c_idle.done); >> + c_idle.idle = fork_idle(cpu); >> >> if (IS_ERR(c_idle.idle)) { >> printk("failed fork for CPU %d\n", cpu); >> - destroy_work_on_stack(&c_idle.work); >> + // destroy_work_on_stack(&c_idle.work); >> return PTR_ERR(c_idle.idle); >> } >> >> @@ -831,7 +832,7 @@ do_rest: >> smpboot_restore_warm_reset_vector(); >> } >> >> - destroy_work_on_stack(&c_idle.work); >> + // destroy_work_on_stack(&c_idle.work); >> return boot_error; >> } >> >> --- >> >> > >> > Thanks, >> > >> > Ingo > > -- 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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