linux-kernel - Re: [RFC PATCH 00/11] sched: CFS low-latency features

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Message-ID: <alpine.LFD.2.00.1008262306140.2768@localhost.localdomain>
Date:	Thu, 26 Aug 2010 23:25:39 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tony Lindgren <tony@...mide.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [RFC PATCH 00/11] sched: CFS low-latency features

On Thu, 26 Aug 2010, Peter Zijlstra wrote:
> 
> Fudging fork seems dubious at best, it seems generated by the use of
> timer_create(.evp->sigev_notify = SIGEV_THREAD), which is a really
> broken thing to do, it has very ill defined semantics and is utterly
> unable to properly cope with error cases. Furthermore its trivial to
> actually correctly implement the desired behaviour, so I'm really
> skeptical on this front; friends don't let friends use SIGEV_THREAD.

SIGEV_THREAD is the best proof that the whole posix timer interface
was comitte[e]d under the influence of not to be revealed
mind-altering substances.

I completely object to add timer specific wakeup magic and support for
braindead fork orgies to the kernel proper. All that mess can be fixed
in user space by using sensible functionality.

Providing support for misdesigned crap just for POSIX compliance
reasons and to make some of the blind abusers of that very same crap
happy would be a completely stupid decision.

In fact that would make a brilliant precedence case for forcing the
kernel to solve user space madness at the expense of kernel
complexity. If we follow down that road we get requests for extra
functionality for AIO, networking and whatever in a split second with
no real good reason to reject them anymore.

Thanks,

	tglx
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