Messages in this thread Patch in this message |  | | Date | Thu, 1 Mar 2012 16:33:49 -0800 | Subject | Re: [PATCH] Extend mwait idle to optimize away CAL and RES interrupts to an idle CPU -v1 | From | Venki Pallipadi <> |
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On Wed, Feb 22, 2012 at 11:50 PM, Ingo Molnar <mingo@elte.hu> wrote: > > * Venkatesh Pallipadi <venki@google.com> wrote: > >> * Do we need some accounting for these wakeups exported for powertop? > > If then tracepoints. > >> * We can also eliminate TS_POLLING flag in favor of this. But, that will have >> a lot more touchpoints and better done as a standlone change. > > Should most definitely be done for this series to be acceptble - > as a preparatory patch in the series, with the feature at the > end of the series. > >> +DECLARE_PER_CPU(atomic_t *, idle_task_ti_flags); > > That's ugly, we should access the idle task's ti flags directly. > > To have efficient percpu access to the idle threads another > clean-up is needed: we should turn idle_thread_array into a > full-structure PER_CPU area. > > For that we need a small variant of fork_idle(), which does not > dup the init thread - pretty trivial.
OK. I looked a bit deeper into this and I understand what you suggested above.
> > 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?
Also, I tried this silly test patch (Cut and paste... Sorry) and it seemed to work fine both with and without CPU hotplug.
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@vger.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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