linux-kernel - RE: Bug 71331 - mlock yields processor to lower priority process

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Message-ID: <1395407680.6030.81.camel@marge.simpson.net>
Date:	Fri, 21 Mar 2014 14:14:40 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	jimmie.davis@...com.com
Cc:	artem_fetishev@...m.com, peterz@...radead.org,
	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: RE: Bug 71331 - mlock yields processor to lower priority process

On Fri, 2014-03-21 at 12:18 +0000, jimmie.davis@...com.com wrote:

> As the submitter of the bug, let me give you my perspective.
> SCHED_FIFO means run my task until it blocks or a higher priority task
> pre-empts it.  Period.

It blocked.
> 
> mlock() doesn't block. check the man page.
> 
I don't see that specified.

(or how it could be, but what do I know, IANIPL)

> Any other way and you are not able to use priority based scheduling. 

Sure you can, allocate and lock down resources before entering critical
sections.

If you think donning a SCHED_FIFO super-suit should make your task
unstoppable, you're gonna be very disappointed.  Fact is if your
Juggernaut bumps ever so gently into a contended sleeping variety lock
(and in the rt kernel that means nearly every lock), it will block.

-Mike

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