linux-kernel - Re: [PATCH v3] sched/fair: Add advisory flag for borrowing a timeslice

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Date:	Tue, 25 Nov 2014 07:52:25 -0700
From:	Khalid Aziz <khalid.aziz@...cle.com>
To:	Rik van Riel <riel@...hat.com>, tglx@...utronix.de, corbet@....net,
	mingo@...hat.com, hpa@...or.com, peterz@...radead.org,
	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,
	avagin@...nvz.org, gorcunov@...nvz.org, serge.hallyn@...onical.com,
	athorlton@....com, oleg@...hat.com, vdavydov@...allels.com,
	daeseok.youn@...il.com, keescook@...omium.org,
	yangds.fnst@...fujitsu.com, sbauer@....utah.edu,
	vishnu.ps@...sung.com, axboe@...com, paulmck@...ux.vnet.ibm.com
CC:	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

On 11/24/2014 07:03 PM, Rik van Riel wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 11/24/2014 03:56 PM, Khalid Aziz wrote:
>> sched/fair: Add advisory flag for borrowing a timeslice
>>
>> This patch adds a way for a task to request to borrow one
>> timeslice from future if it is about to be preempted, so it could
>> delay preemption and complete any critical task it is in the middle
>> of.
>>
>> This feature helps with performance on databases and has been used
>> for many years on other OSs by the databases. This feature helps in
>> situation where a task acquires a lock before performing a critical
>> operation on the database and happens to get preempted
>
> Why don't the other tasks that want the lock sleep on the
> lock?
>
> I can see this "solution" help mostly with userspace spinlocks,
> which are relics of a past era that need to die. There is no
> way userspace spinlocks will not fail miserably on virtual
> machines, and it is time to get rid of them.

This solution indeed is for userspace spinlocks. Database code has been 
written with all critical locking implemented in userspace (as I have 
been told by database folks. I am not a database guy).

--
Khalid

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