Messages in this thread | | | Date | Fri, 27 May 2011 15:01:38 +0800 | Subject | Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM | From | Yong Zhang <> |
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On Fri, May 27, 2011 at 1:23 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > We'd end up with something like the below, which isn't too different > from what I've now got queued. > > It has the extra cpu == smp_processor_id() check, but I'm not sure this > whole case is worth the trouble. I could go stick some counters in to > verify how often all this happens I guess. > > --- > arch/x86/include/asm/system.h | 2 ++ > kernel/sched.c | 14 +++++++++++--- > kernel/sched_debug.c | 7 +++++++ > 3 files changed, 20 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h > index c2ff2a1..2c597e8 100644 > --- a/arch/x86/include/asm/system.h > +++ b/arch/x86/include/asm/system.h > @@ -10,6 +10,8 @@ > #include <linux/kernel.h> > #include <linux/irqflags.h> > > +#define __ARCH_WANT_INTERRUPTS_ON_CTXSW > + > /* entries in ARCH_DLINFO: */ > #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64) > # define AT_VECTOR_SIZE_ARCH 2 > diff --git a/kernel/sched.c b/kernel/sched.c > index 2d12893..e4f7a9f 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2636,9 +2636,17 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > * to spin on ->on_cpu if p is current, since that would > * deadlock. > */ > - if (p == current) { > - ttwu_queue(p, cpu); > - goto stat; > + if (cpu == smp_processor_id()) { > + struct rq *rq; > + > + rq = __task_rq_lock(p); > + if (p->on_cpu) {
As Oleg has said, I also think we don't need this check.
> + ttwu_activate(rq, p, ENQUEUE_WAKEUP); > + ttwu_do_wakeup(rq, p, wake_flags);
And the difference with ttwu_queue() is ttwu_queue() calls ttwu_activate() with another flag ENQUEUE_WAKING, so if we call ->task_waking() before ttwu_queue(), I guess it will work too. But I like this version, because we call ->task_waking() and ttwu_activate() on the local cpu, that means the calculations on vruntime in that two functions are accumulated into noop.
Thanks, Yong
> + __task_rq_unlock(rq); > + goto stat; > + } > + __task_rq_unlock(rq); > } > #endif > cpu_relax(); > diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c > index a6710a1..f0ff1de 100644 > --- a/kernel/sched_debug.c > +++ b/kernel/sched_debug.c > @@ -332,6 +332,13 @@ static int sched_debug_show(struct seq_file *m, void *v) > (int)strcspn(init_utsname()->version, " "), > init_utsname()->version); > > +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW > + SEQ_printf(m, "__ARCH_WANT_INTERRUPTS_ON_CTXSW\n"); > +#endif > +#ifdef __ARCH_WANT_UNLOCKED_CTXSW > + SEQ_printf(m, "__ARCH_WANT_UNLOCKED_CTXSW\n"); > +#endif > + > #define P(x) \ > SEQ_printf(m, "%-40s: %Ld\n", #x, (long long)(x)) > #define PN(x) \ > > >
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