From: Jason Low <jason.low2@hp.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Lai Jiangshan <laijs@cn.fujitsu.com>
Subject: Re: [patch 6/6] rtmutex: Avoid pointless requeueing in the deadlock detection chain walk
Date: Tue, 27 May 2014 15:49:21 -0700 [thread overview]
Message-ID: <CAGQ1y=6DOs0hcdV+NvOdA9hxf6kwu-R0M-c6R2iUK4ufr=pwEg@mail.gmail.com> (raw)
In-Reply-To: <20140522031950.280830190@linutronix.de>
On Wed, May 21, 2014 at 8:25 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> @@ -440,32 +452,41 @@ static int rt_mutex_adjust_prio_chain(st
> get_task_struct(task);
> raw_spin_lock_irqsave(&task->pi_lock, flags);
>
> - if (waiter == rt_mutex_top_waiter(lock)) {
> - /*
> - * The waiter became the top waiter on the
> - * lock. Remove the previous top waiter from the tasks
> - * pi waiters list and add waiter to it.
> - */
> - rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
> - rt_mutex_enqueue_pi(task, waiter);
> - __rt_mutex_adjust_prio(task);
> -
> - } else if (prerequeue_top_waiter == waiter) {
> - /*
> - * The waiter was the top waiter on the lock. Remove
> - * waiter from the tasks pi waiters list and add the
> - * new top waiter to it.
> - */
> - rt_mutex_dequeue_pi(task, waiter);
> - waiter = rt_mutex_top_waiter(lock);
> - rt_mutex_enqueue_pi(task, waiter);
> - __rt_mutex_adjust_prio(task);
> -
> - } else {
> - /*
> - * Nothing changed. No need to do any priority
> - * adjustment.
> - */
> + /*
> + * In case we are just following the lock chain for deadlock
> + * detection we can avoid the whole requeue and priority
> + * adjustment business.
> + */
> + if (requeue) {
> + if (waiter == rt_mutex_top_waiter(lock)) {
> + /*
> + * The waiter became the top waiter on the
> + * lock. Remove the previous top waiter from
> + * the tasks pi waiters list and add waiter to
> + * it.
> + */
> + rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
> + rt_mutex_enqueue_pi(task, waiter);
> + __rt_mutex_adjust_prio(task);
> +
> + } else if (prerequeue_top_waiter == waiter) {
> + /*
> + * The waiter was the top waiter on the
> + * lock. Remove waiter from the tasks pi
> + * waiters list and add the new top waiter to
> + * it.
> + */
> + rt_mutex_dequeue_pi(task, waiter);
> + waiter = rt_mutex_top_waiter(lock);
> + rt_mutex_enqueue_pi(task, waiter);
> + __rt_mutex_adjust_prio(task);
> +
> + } else {
> + /*
> + * Nothing changed. No need to do any priority
> + * adjustment.
> + */
> + }
> }
>
> raw_spin_unlock_irqrestore(&task->pi_lock, flags);
In the above case, could we go 1 step further and avoid taking the pi
lock as well?
if (requeue) {
raw_spin_lock_irqsave(&task->pi_lock, flags);
if (waiter == rt_mutex_top_waiter(lock)) {
/*
* The waiter became the top waiter on the
* lock. Remove the previous top waiter from
* the tasks pi waiters list and add waiter to
* it.
*/
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
} else if (prerequeue_top_waiter == waiter) {
/*
* The waiter was the top waiter on the
* lock. Remove waiter from the tasks pi
* waiters list and add the new top waiter to
* it.
*/
rt_mutex_dequeue_pi(task, waiter);
waiter = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
} else {
/*
* Nothing changed. No need to do any priority
* adjustment.
*/
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
}
next prev parent reply other threads:[~2014-05-27 22:49 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-22 3:25 [patch 0/6] rtmutex: Repair deadlock detector and cleanup Thomas Gleixner
2014-05-22 3:25 ` [patch 1/6] rtmutex: Fix deadlock detector for real Thomas Gleixner
2014-05-27 22:09 ` Steven Rostedt
2014-05-28 9:57 ` Thomas Gleixner
2014-05-28 19:28 ` [tip:core/urgent] " tip-bot for Thomas Gleixner
2014-05-22 3:25 ` [patch 2/6] rtmutex: Remove builtin tester Thomas Gleixner
2014-05-30 21:36 ` Steven Rostedt
2014-05-22 3:25 ` [patch 3/6] rtmutex: Cleanup deadlock detector debug logic Thomas Gleixner
2014-05-30 22:08 ` Steven Rostedt
2014-06-21 20:32 ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-05-22 3:25 ` [patch 4/6] rtmutex: Confine deadlock logic to futex Thomas Gleixner
2014-05-22 7:10 ` Peter Zijlstra
2014-05-28 20:28 ` Thomas Gleixner
2014-05-31 2:06 ` Steven Rostedt
2014-05-22 3:25 ` [patch 5/6] rtmutex: Clarify the lock chain walk Thomas Gleixner
2014-05-31 2:19 ` Steven Rostedt
2014-05-22 3:25 ` [patch 6/6] rtmutex: Avoid pointless requeueing in the deadlock detection " Thomas Gleixner
2014-05-27 22:49 ` Jason Low [this message]
2014-05-28 9:43 ` Thomas Gleixner
2014-05-31 2:21 ` Steven Rostedt
2014-06-21 20:33 ` [tip:locking/core] " tip-bot for Thomas Gleixner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAGQ1y=6DOs0hcdV+NvOdA9hxf6kwu-R0M-c6R2iUK4ufr=pwEg@mail.gmail.com' \
--to=jason.low2@hp.com \
--cc=laijs@cn.fujitsu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).