linux-kernel - Re: [PATCH 1/7] locking/rwsem: don't resched at the end of optimistic spinning

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <53DFD2B3.3090101@hp.com>
Date:	Mon, 04 Aug 2014 14:36:35 -0400
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
	Davidlohr Bueso <davidlohr@...com>,
	Jason Low <jason.low2@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 1/7] locking/rwsem: don't resched at the end of optimistic
 spinning

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/