linux-kernel - Re: [RFC][PATCH 0/5] preempt

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Message-ID: <20130814164827.GN23412@tassilo.jf.intel.com>
Date:	Wed, 14 Aug 2013 09:48:27 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH 0/5] preempt_count rework

On Wed, Aug 14, 2013 at 03:15:39PM +0200, Peter Zijlstra wrote:
> These patches optimize preempt_enable by firstly folding the preempt and
> need_resched tests into one -- this should work for all architectures. And
> secondly by providing per-arch preempt_count implementations; with x86 using
> per-cpu preempt_count for fastest access.
> 
> These patches have so far only been compiled for defconfig-x86_64 +
> CONFIG_PREEMPT=y and boot tested with kvm -smp 4 upto wanting to mount root.
> 
> It still needs asm volatile("call preempt_schedule": : :"memory"); as per
> Andi's other patches to avoid the C calling convention cluttering the
> preempt_enable() sites.

FWIW I removed the user_schedule in v2 because I don't need it anymore.
Feel free to pick it up from v1 though.

It needs two patches: the one adding SAVE_ALL for 32bit and
the parts of the put_user() patch adding user_schedule

When it's not used in user_ anymore it should probably 
be renamed too, to preempt_schedule or somesuch,
and probably moved to a different file.

-Andi

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