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: <5473E388.6000605@redhat.com>
Date:	Mon, 24 Nov 2014 21:03:52 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Khalid Aziz <khalid.aziz@...cle.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
 (was: Pre-emption control for userspace)

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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.

- -- 
All rights reversed
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