linux-kernel - Re: [PATCH] rtmutex: ensure only the top waiter or higher priority task can take the lock and reduce unrelated boosting

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Message-ID: <4D0A77B5.3040900@linux.intel.com>
Date:	Thu, 16 Dec 2010 12:33:57 -0800
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Lai Jiangshan <eag0628@...il.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <hidave.darkstar@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] rtmutex: ensure only the top waiter or higher priority
 task can take the lock and reduce unrelated boosting

On 12/15/2010 06:24 AM, Lai Jiangshan wrote:
> On Wed, Dec 15, 2010 at 8:07 PM, Thomas Gleixner<tglx@...utronix.de>  wrote:
>> On Wed, 15 Dec 2010, Lai Jiangshan wrote:
>>> +     if (waiter || rt_mutex_has_waiters(lock)) {
>>> +             unsigned long flags;
>>> +             struct rt_mutex_waiter *top;
>>> +
>>> +             raw_spin_lock_irqsave(&task->pi_lock, flags);
>>> +
>>> +             /* remove the queued waiter. */
>>> +             if (waiter) {
>>> +                     plist_del(&waiter->list_entry,&lock->wait_list);
>>> +                     task->pi_blocked_on = NULL;
>>> +             }
>>> +
>>> +             /*
>>> +              * We have to enqueue the top waiter(if have) into
>>> +              * task->pi_waiters list and would get boost from it.
>>
>> No, we don't get boosted from it. We just have to enqueue it into
>> pi_waiters list. There is no boosting happening at this point. Please
>> be very careful with the comments in this code.
>>
>> Otherwise this looks really interesting. Still this wants to be ported
>> to -rt and stress tested there.
>>
>
> Hi, Thomas,
>
> Where can I find the code of stress testcases?

See http://rt.wiki.kernel.org, There are several benchmarks available 
for RT there.

I believe there are some built-int rt-mutex testers as well:\
CONFIG_RT_MUTEX_TESTER

-- 
Darren Hart
Yocto Linux Kernel
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