From: Waiman Long <waiman.long-VXdhtT5mjnY@public.gmane.org>
To: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Davidlohr Bueso <davidlohr-VXdhtT5mjnY@public.gmane.org>,
Jason Low <jason.low2-VXdhtT5mjnY@public.gmane.org>,
Scott J Norton <scott.norton-VXdhtT5mjnY@public.gmane.org>
Subject: Re: [PATCH 1/7] locking/rwsem: don't resched at the end of optimistic spinning
Date: Mon, 04 Aug 2014 14:36:35 -0400 [thread overview]
Message-ID: <53DFD2B3.3090101@hp.com> (raw)
In-Reply-To: <20140804075528.GI9918-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
On 08/04/2014 03:55 AM, Peter Zijlstra wrote:
> On Sun, Aug 03, 2014 at 10:36:16PM -0400, Waiman Long wrote:
>> For a fully preemptive kernel, a call to preempt_enable() could
>> potentially trigger a task rescheduling event. In the case of rwsem
>> optimistic spinning, the task has either gotten the lock or is going
>> to sleep soon. So there is no point to do rescheduling here.
> Uh what? Why shouldn't we preempt if we've gotten the lock? What if a
> FIFO task just woke up?
I didn't mean that we shouldn't preempt if there is a higher priority
task. I am sure that there will be other preemption points along the way
that a higher priority task can take over the CPU. I just want to say
that doing it here may not be the best place especially if the task is
going to sleep soon.
If you think this patch does not make sense, I can remove it as other
patches in the set has no dependency on this one.
-Longman
next prev parent reply other threads:[~2014-08-04 18:36 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-04 2:36 [PATCH 0/7] locking/rwsem: enable reader opt-spinning & writer respin Waiman Long
2014-08-04 2:36 ` [PATCH 1/7] locking/rwsem: don't resched at the end of optimistic spinning Waiman Long
2014-08-04 7:55 ` Peter Zijlstra
[not found] ` <20140804075528.GI9918-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2014-08-04 18:36 ` Waiman Long [this message]
2014-08-04 20:48 ` Peter Zijlstra
2014-08-04 21:12 ` Jason Low
2014-08-05 17:54 ` Waiman Long
2014-08-04 2:36 ` [PATCH 3/7] locking/rwsem: check for active writer/spinner before wakeup Waiman Long
[not found] ` <1407119782-41119-4-git-send-email-Waiman.Long-VXdhtT5mjnY@public.gmane.org>
2014-08-04 21:20 ` Jason Low
2014-08-05 17:56 ` Waiman Long
2014-08-04 2:36 ` [PATCH 4/7] locking/rwsem: threshold limited spinning for active readers Waiman Long
[not found] ` <1407119782-41119-5-git-send-email-Waiman.Long-VXdhtT5mjnY@public.gmane.org>
2014-08-05 4:54 ` Davidlohr Bueso
2014-08-05 5:30 ` Davidlohr Bueso
[not found] ` <1407216632.2566.22.camel-5JQ4ckphU/8SZAcGdq5asR6epYMZPwEe5NbjCUgZEJk@public.gmane.org>
2014-08-05 5:41 ` Davidlohr Bueso
2014-08-05 18:14 ` Waiman Long
2014-08-04 2:36 ` [PATCH 5/7] locking/rwsem: move down rwsem_down_read_failed function Waiman Long
2014-08-04 2:36 ` [PATCH 6/7] locking/rwsem: enables optimistic spinning for readers Waiman Long
2014-08-04 2:36 ` [PATCH 7/7] locking/rwsem: allow waiting writers to go back to optimistic spinning Waiman Long
[not found] ` <1407119782-41119-1-git-send-email-Waiman.Long-VXdhtT5mjnY@public.gmane.org>
2014-08-04 2:36 ` [PATCH 2/7] locking/rwsem: more aggressive use of " Waiman Long
2014-08-04 4:09 ` Davidlohr Bueso
[not found] ` <1407119782-41119-3-git-send-email-Waiman.Long-VXdhtT5mjnY@public.gmane.org>
2014-08-04 4:10 ` Jason Low
2014-08-04 4:25 ` [PATCH 0/7] locking/rwsem: enable reader opt-spinning & writer respin Davidlohr Bueso
[not found] ` <1407126313.3216.10.camel-5JQ4ckphU/8SZAcGdq5asR6epYMZPwEe5NbjCUgZEJk@public.gmane.org>
2014-08-04 18:07 ` Waiman Long
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