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Date: Mon, 7 Jan 2013 17:12:47 -0800
From: Neil Zhang <zhangwm@...vell.com>
To: Mike Galbraith <bitbucket@...ine.de>
CC: "mingo@...nel.org" <mingo@...nel.org>,
"peterz@...radead.org" <peterz@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] sched: remove redundant update_runtime notifier
Mike,
> -----Original Message-----
> From: Mike Galbraith [mailto:bitbucket@...ine.de]
> Sent: 2013年1月7日 18:40
> To: Neil Zhang
> Cc: mingo@...nel.org; peterz@...radead.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] sched: remove redundant update_runtime notifier
>
> On Fri, 2012-12-28 at 18:00 +0800, Neil Zhang wrote:
> > migration_call() will do all the things that update_runtime() does.
> > So it seems update_runtime() is a redundant notifier, remove it.
> >
> > Furthermore, there is potential risk that the current code will catch
> > BUG_ON at line 687 of rt.c when do cpu hotplug while there are
> > realtime threads running because of enable runtime twice.
>
> Hm, box must be reading lkml behind my back.
>
> PID: 14735 TASK: ffff880e75e86500 CPU: 4 COMMAND: "reboot"
> #0 [ffff880e74b3d890] machine_kexec at ffffffff8102676e
> #1 [ffff880e74b3d8e0] crash_kexec at ffffffff810a3a3a
> #2 [ffff880e74b3d9b0] oops_end at ffffffff81446238
> #3 [ffff880e74b3d9d0] do_invalid_op at ffffffff810035d4
> #4 [ffff880e74b3da70] invalid_op at ffffffff8144d9bb
> [exception RIP: __disable_runtime+494] <== BUG_ON(want);
> RIP: ffffffff81045dae RSP: ffff880e74b3db28 RFLAGS: 00010082
> RAX: 000000000000046a RBX: ffff880e7fcd1310 RCX:
> ffffffff81d88a90
> RDX: 000000000000046a RSI: 0000000000000050 RDI:
> ffff880e7fcd19b0
> RBP: ffff880e74b3db98 R8: 0000000000000010 R9:
> ffff88047f423408
> R10: 0000000000000050 R11: ffffffff81250190 R12:
> 0000000000000050
> R13: fffffffffde9f140 R14: ffff880e7fcd1310 R15:
> 000000000000122f
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> #5 [ffff880e74b3dba0] rq_offline_rt at ffffffff8104b36a
> #6 [ffff880e74b3dbc0] set_rq_offline at ffffffff81043c9e
> #7 [ffff880e74b3dbe0] rq_attach_root at ffffffff8104c130
> #8 [ffff880e74b3dc10] cpu_attach_domain at ffffffff81054f44
> #9 [ffff880e74b3dc80] build_sched_domains at ffffffff81055525
> #10 [ffff880e74b3dcd0] partition_sched_domains at ffffffff81055835
> #11 [ffff880e74b3dd70] cpuset_cpu_inactive at ffffffff81055a0d
> #12 [ffff880e74b3dd80] notifier_call_chain at ffffffff81448907
> #13 [ffff880e74b3ddb0] _cpu_down at ffffffff8142b57b
> #14 [ffff880e74b3de10] disable_nonboot_cpus at ffffffff8105ba23
> #15 [ffff880e74b3de40] kernel_restart at ffffffff81071dde
> #16 [ffff880e74b3de50] sys_reboot at ffffffff81071fc3
> #17 [ffff880e74b3df80] system_call_fastpath at ffffffff8144ca12
> RIP: 00007fed35778316 RSP: 00007fff23f7e198 RFLAGS: 00010202
> RAX: 00000000000000a9 RBX: ffffffff8144ca12 RCX:
> 00007fed35771130
> RDX: 0000000001234567 RSI: 0000000028121969 RDI:
> fffffffffee1dead
> RBP: 0000000000000000 R8: 0000000000020fd0 R9:
> 000000000060d120
> R10: 00007fff23f7df40 R11: 0000000000000202 R12:
> 0000000000000000
> R13: 0000000000000000 R14: 0000000000000001 R15:
> 0000000000000000
> ORIG_RAX: 00000000000000a9 CS: 0033 SS: 002b
>
So, it seems my first patch is still needed, we should avoid enable runtime twice in case the value is changed between the two times.
> > Cc: bitbucket@...ine.de
> > Signed-off-by: Neil Zhang <zhangwm@...vell.com>
> > ---
> > kernel/sched/core.c | 3 ---
> > kernel/sched/rt.c | 40 ----------------------------------------
> > kernel/sched/sched.h | 1 -
> > 3 files changed, 0 insertions(+), 44 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c index
> > 257002c..7b6a4d8 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -6779,9 +6779,6 @@ void __init sched_init_smp(void)
> > hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
> > hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
> >
> > - /* RT runtime code needs to handle some hotplug events */
> > - hotcpu_notifier(update_runtime, 0);
> > -
> > init_hrtick();
> >
> > /* Move init over to a non-isolated CPU */ diff --git
> > a/kernel/sched/rt.c b/kernel/sched/rt.c index 418feb0..1a499d2 100644
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -697,15 +697,6 @@ balanced:
> > }
> > }
> >
> > -static void disable_runtime(struct rq *rq) -{
> > - unsigned long flags;
> > -
> > - raw_spin_lock_irqsave(&rq->lock, flags);
> > - __disable_runtime(rq);
> > - raw_spin_unlock_irqrestore(&rq->lock, flags);
> > -}
> > -
> > static void __enable_runtime(struct rq *rq) {
> > rt_rq_iter_t iter;
> > @@ -730,37 +721,6 @@ static void __enable_runtime(struct rq *rq)
> > }
> > }
> >
> > -static void enable_runtime(struct rq *rq) -{
> > - unsigned long flags;
> > -
> > - raw_spin_lock_irqsave(&rq->lock, flags);
> > - __enable_runtime(rq);
> > - raw_spin_unlock_irqrestore(&rq->lock, flags);
> > -}
> > -
> > -int update_runtime(struct notifier_block *nfb, unsigned long action,
> > void *hcpu) -{
> > - int cpu = (int)(long)hcpu;
> > -
> > - switch (action) {
> > - case CPU_DOWN_PREPARE:
> > - case CPU_DOWN_PREPARE_FROZEN:
> > - disable_runtime(cpu_rq(cpu));
> > - return NOTIFY_OK;
> > -
> > - case CPU_DOWN_FAILED:
> > - case CPU_DOWN_FAILED_FROZEN:
> > - case CPU_ONLINE:
> > - case CPU_ONLINE_FROZEN:
> > - enable_runtime(cpu_rq(cpu));
> > - return NOTIFY_OK;
> > -
> > - default:
> > - return NOTIFY_DONE;
> > - }
> > -}
> > -
> > static int balance_runtime(struct rt_rq *rt_rq) {
> > int more = 0;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index
> > fc88644..16d18a1 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -890,7 +890,6 @@ extern void sysrq_sched_debug_show(void);
> extern
> > void sched_init_granularity(void); extern void
> > update_max_interval(void); extern void update_group_power(struct
> > sched_domain *sd, int cpu); -extern int update_runtime(struct
> > notifier_block *nfb, unsigned long action, void *hcpu); extern void
> > init_sched_rt_class(void); extern void init_sched_fair_class(void);
> >
>
Best Regards,
Neil Zhang
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