From: Mike Galbraith <efault@gmx.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
Manfred Spraul <manfred@colorfullife.com>
Subject: Re: [PATCH -rt] ipc/sem: Rework semaphore wakeups
Date: Wed, 14 Sep 2011 15:02:19 +0200 [thread overview]
Message-ID: <1316005339.6497.0.camel@marge.simson.net> (raw)
In-Reply-To: <1315994224.5040.1.camel@twins>
All better.
On Wed, 2011-09-14 at 11:57 +0200, Peter Zijlstra wrote:
> Subject: ipc/sem: Rework semaphore wakeups
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Tue Sep 13 15:09:40 CEST 2011
>
> Current sysv sems have a weird ass wakeup scheme that involves keeping
> preemption disabled over a potential O(n^2) loop and busy waiting on
> that on other CPUs.
>
> Kill this and simply wake the task directly from under the sem_lock.
>
> This was discovered by a migrate_disable() debug feature that
> disallows:
>
> spin_lock();
> preempt_disable();
> spin_unlock()
> preempt_enable();
>
> Cc: Manfred Spraul <manfred@colorfullife.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Reported-by: Mike Galbraith <efault@gmx.de>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> ipc/sem.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> Index: linux-rt/ipc/sem.c
> ===================================================================
> --- linux-rt.orig/ipc/sem.c
> +++ linux-rt/ipc/sem.c
> @@ -415,6 +415,13 @@ static int try_atomic_semop (struct sem_
> static void wake_up_sem_queue_prepare(struct list_head *pt,
> struct sem_queue *q, int error)
> {
> +#ifdef CONFIG_PREEMPT_RT_BASE
> + struct task_struct *p = q->sleeper;
> + get_task_struct(p);
> + q->status = error;
> + wake_up_process(p);
> + put_task_struct(p);
> +#else
> if (list_empty(pt)) {
> /*
> * Hold preempt off so that we don't get preempted and have the
> @@ -426,6 +433,7 @@ static void wake_up_sem_queue_prepare(st
> q->pid = error;
>
> list_add_tail(&q->simple_list, pt);
> +#endif
> }
>
> /**
> @@ -439,6 +447,7 @@ static void wake_up_sem_queue_prepare(st
> */
> static void wake_up_sem_queue_do(struct list_head *pt)
> {
> +#ifndef CONFIG_PREEMPT_RT_BASE
> struct sem_queue *q, *t;
> int did_something;
>
> @@ -451,6 +460,7 @@ static void wake_up_sem_queue_do(struct
> }
> if (did_something)
> preempt_enable();
> +#endif
> }
>
> static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
>
next prev parent reply other threads:[~2011-09-14 13:02 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-10 9:12 [ANNOUNCE] 3.0.4-rt13 Thomas Gleixner
2011-09-10 14:53 ` Madovsky
2011-09-10 17:27 ` Rolando Martins
2011-09-11 10:35 ` Mike Galbraith
2011-09-11 17:01 ` Mike Galbraith
2011-09-12 7:24 ` Thomas Gleixner
2011-09-12 8:59 ` Peter Zijlstra
2011-09-12 9:05 ` Mike Galbraith
2011-09-12 13:52 ` Mike Galbraith
2011-09-12 14:53 ` Mike Galbraith
2011-09-13 13:36 ` Peter Zijlstra
2011-09-13 15:17 ` Mike Galbraith
2011-09-13 15:08 ` Peter Zijlstra
2011-09-13 15:28 ` Mike Galbraith
2011-09-13 16:13 ` Peter Zijlstra
2011-09-21 10:17 ` rt14: strace -> migrate_disable_atomic imbalance Mike Galbraith
2011-09-21 17:01 ` Peter Zijlstra
2011-09-21 18:50 ` Peter Zijlstra
2011-09-22 4:46 ` Mike Galbraith
2011-09-22 6:31 ` Peter Zijlstra
2011-09-22 8:38 ` Peter Zijlstra
2011-09-22 10:00 ` Peter Zijlstra
2011-09-22 11:55 ` Mike Galbraith
2011-09-22 12:09 ` Peter Zijlstra
2011-09-22 13:42 ` Mike Galbraith
2011-09-22 14:05 ` Mike Galbraith
2011-09-22 15:20 ` Peter Zijlstra
2011-09-22 14:34 ` Peter Zijlstra
2011-09-22 14:38 ` Mike Galbraith
2011-09-22 14:41 ` Mike Galbraith
2011-09-22 14:41 ` Peter Zijlstra
2011-09-22 14:46 ` Mike Galbraith
2011-09-22 11:31 ` Peter Zijlstra
2011-09-22 11:46 ` Peter Zijlstra
2011-09-22 14:52 ` Oleg Nesterov
2011-09-22 15:13 ` Peter Zijlstra
2011-09-14 9:57 ` [PATCH -rt] ipc/sem: Rework semaphore wakeups Peter Zijlstra
2011-09-14 13:02 ` Mike Galbraith [this message]
2011-09-14 18:48 ` Manfred Spraul
2011-09-14 19:23 ` Peter Zijlstra
2011-09-15 17:04 ` Manfred Spraul
2011-09-12 10:04 ` [ANNOUNCE] 3.0.4-rt13 Peter Zijlstra
2011-09-12 11:33 ` Mike Galbraith
2011-09-11 18:14 ` Mike Galbraith
2011-09-12 7:33 ` Thomas Gleixner
2011-09-12 8:05 ` Mike Galbraith
2011-09-12 8:43 ` Mike Galbraith
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