linux-kernel - Re: [PATCH v3] sched/fair: Add advisory flag for borrowing a timeslice (was: Pre-emption control for userspace)

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Message-ID: <20141125101238.GA19795@linux.vnet.ibm.com>
Date:	Tue, 25 Nov 2014 15:42:38 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Khalid Aziz <khalid.aziz@...cle.com>
Cc:	tglx@...utronix.de, corbet@....net, mingo@...hat.com,
	hpa@...or.com, peterz@...radead.org, riel@...hat.com,
	akpm@...ux-foundation.org, rientjes@...gle.com, ak@...ux.intel.com,
	mgorman@...e.de, liwanp@...ux.vnet.ibm.com, raistlin@...ux.it,
	kirill.shutemov@...ux.intel.com, atomlin@...hat.com,
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	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v3] sched/fair: Add advisory flag for borrowing a
 timeslice (was: Pre-emption control for userspace)

> 
> - Request to borrow timeslice is not guranteed to be honored.
> - If the task is allowed to borrow, kernel will inform the task
>   of this. When this happens, task must yield the processor as soon
>   as it completes its critical section.
> - If the task fails to yield processor after being allowed to
>   borrow, it is penalized by forcing it to skip its next time slot
>   by the scheduler.
> - Task is charged additional time for the borrowed timeslice as
>   accumulated run time. This pushes it further down in consideration
>   for the next task to run.
> 

Is there a way for us to identify if the lock is contended?
Because it may not be prudent to allow a task to borrow timeslice for a
lock which isnt contended.

-- 
Thanks and Regards
Srikar Dronamraju

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