linux-kernel - Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing a timeslice

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Date:	Fri, 19 Dec 2014 00:02:29 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Khalid Aziz <khalid.aziz@...cle.com>
cc:	Peter Zijlstra <peterz@...radead.org>, corbet@....net,
	mingo@...hat.com, hpa@...or.com, riel@...hat.com,
	akpm@...ux-foundation.org, rientjes@...gle.com, ak@...ux.intel.com,
	mgorman@...e.de, 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,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing
 a timeslice

On Thu, 18 Dec 2014, Khalid Aziz wrote:
> On 12/18/2014 03:28 PM, Peter Zijlstra wrote:
> > On Thu, Dec 18, 2014 at 11:44:19AM -0700, Khalid Aziz wrote:
> > > sched/fair: Add advisory flag for borrowing a timeslice
> > 
> > yuck hatred and much of that.
> > 
> > Also, you fail to explain why a kernel side spin futex-lock is not an
> > option.
> > 
> 
> I had explained that when this question came up in the last round of
> discussions. The queuing problem I am trying to solve stems from userspace
> locks. Java and databases implement their own userspace locks that do not use
> futex. Solving this with futex will not help the primary users of this
> solution.

If we can solve it with a proper designed and well thought out
functionality in the kernel based on a futex like mechanism, why cant
java and databases not switch over to that and simply use it?

You need to modify user space anyway, so it does not matter whether
you modify it in a sane or in a hacky way.

But its simpler to hack crap into the scheduler than coming up with a
proper solution to the problem, right?

> Hope this helps.

Not at all.

Thanks,

	tglx
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