| Message ID | 1306430633.2497.91.camel@laptop (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 05/26, Peter Zijlstra wrote: > > It has the extra cpu == smp_processor_id() check, but I'm not sure this > whole case is worth the trouble. Agreed, this case is very unlikely. Perhaps it makes the code more clear though, up to you. But, if we keep this check, > @@ -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) { > + ttwu_activate(rq, p, ENQUEUE_WAKEUP); > + ttwu_do_wakeup(rq, p, wake_flags); > + __task_rq_unlock(rq); then why we re-check ->on_cpu? Just curious. Oleg.
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) \ > > >
Peter, On 5/26/2011 10:53 PM, Peter Zijlstra wrote: > On Thu, 2011-05-26 at 19:17 +0200, Peter Zijlstra wrote: >> On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote: >>> On 05/26, Peter Zijlstra wrote: >>>> >>>> @@ -2636,7 +2636,8 @@ 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) { >>>> + if (cpu == smp_processor_id()) { >>>> + p->sched_contributes_to_load = 0; >>>> ttwu_queue(p, cpu); >>> >>> Btw. I do not pretend I really understand se->vruntime, but in this >>> case we are doing enqueue_task() without ->task_waking(), however we >>> pass ENQUEUE_WAKING. Is it correct? >> >> No its not, that's the thing that I got wrong the first time and caused >> these pauses. > > 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. > Are you planning send version of this patch for stable .39 too ? Regards Santosh
On Fri, 2011-05-27 at 20:53 +0530, Santosh Shilimkar wrote: > Peter, > > On 5/26/2011 10:53 PM, Peter Zijlstra wrote: > > On Thu, 2011-05-26 at 19:17 +0200, Peter Zijlstra wrote: > >> On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote: > >>> On 05/26, Peter Zijlstra wrote: > >>>> > >>>> @@ -2636,7 +2636,8 @@ 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) { > >>>> + if (cpu == smp_processor_id()) { > >>>> + p->sched_contributes_to_load = 0; > >>>> ttwu_queue(p, cpu); > >>> > >>> Btw. I do not pretend I really understand se->vruntime, but in this > >>> case we are doing enqueue_task() without ->task_waking(), however we > >>> pass ENQUEUE_WAKING. Is it correct? > >> > >> No its not, that's the thing that I got wrong the first time and caused > >> these pauses. > > > > 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. > > > Are you planning send version of this patch for stable .39 > too ? .39 is fine, as the ttwu() changes only appeared in mainline during the current merge window. Cheers, M.
On 5/27/2011 8:59 PM, Marc Zyngier wrote: > On Fri, 2011-05-27 at 20:53 +0530, Santosh Shilimkar wrote: [..] >> Are you planning send version of this patch for stable .39 >> too ? > > .39 is fine, as the ttwu() changes only appeared in mainline during the > current merge window. > Thanks Marc for info. Regards Santosh
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) { + ttwu_activate(rq, p, ENQUEUE_WAKEUP); + ttwu_do_wakeup(rq, p, wake_flags); + __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) \