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

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Date:	Tue, 23 Dec 2014 11:52:51 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Khalid Aziz <khalid.aziz@...cle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	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


* Khalid Aziz <khalid.aziz@...cle.com> wrote:

> On 12/19/2014 04:57 PM, Thomas Gleixner wrote:
> >On Fri, 19 Dec 2014, Khalid Aziz wrote:
> >>The queuing problem caused by a task taking a contended lock just before its
> >>current timeslice is up which userspace app wouldn't know about, is a real
> >>problem nevertheless.
> >
> >We know that already.
> >
> >>My patch attempts to avoid the contention in the first
> >>place. futex with adaptive spinning is a post-contention solution that tries
> >>to minimize the cost of contention but does nothing to avoid the contention.
> >
> >I never said that adaptive spinning can solve that problem.
> >
> >If you would have carefuly read what I wrote, you might have noticed,
> >that I said:
> >
> >      a proper futex like spin mechanism
> >
> >Can you spot the subtle difference between that phrase and 'futex with
> >adaptive spinning'?
> >
> >>Solving this problem using futex can help only if the userspace lock uses
> >>futex.
> >
> >A really fundamentally new and earth shattering insight.
> >
> >If you would spend your time to actually digest what maintainers are
> >telling you, we might make progress on that matter.
> >
> >But you prefer to spend your time by repeating yourself and providing
> >completely useless information.
> >
> >What you are missing completely here is that neither me nor other
> >maintainers involved care about how you spend your time. But we very
> >much care about the time WE waste with your behaviour.
> 
> I am sorry that you feel the need to continue to resort to 
> personal attacks [...]

Thomas did not attack your person AFAICS - he criticised your 
arguments with increasing volume, because he did not see you 
respond to his arguments in substance.

> even after I made it clear in my last response that I was not 
> going to pursue this patch. There is no possibility of a 
> productive discussion of a solution at this point. [...]

I think there is very much a possibility of a productive 
discussion:

> [...] I hope someone else can find a solution you find 
> acceptable.

to implement what Thomas suggested in the discussion: a proper 
futex like spin mechanism? That looks like a totally acceptable 
solution to me, without the disadvantages of your proposed 
solution.

Thanks,

	Ingo
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