Subject: Re: [PATCH v2 10/12] Maintain preemptability count even for
 !CONFIG_PREEMPT kernels
From: Peter Zijlstra <peterz@infradead.org>
To: Gleb Natapov <gleb@redhat.com>
Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       avi@redhat.com, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com,
       riel@redhat.com
In-Reply-To: <1258985167-29178-11-git-send-email-gleb@redhat.com>
References: <1258985167-29178-1-git-send-email-gleb@redhat.com>
	 <1258985167-29178-11-git-send-email-gleb@redhat.com>
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Date: Mon, 23 Nov 2009 16:34:15 +0100
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On Mon, 2009-11-23 at 16:06 +0200, Gleb Natapov wrote:
> Do not preempt kernel. Just maintain counter to know if task can be rescheduled.
> Asynchronous page fault may be delivered while spinlock is held or current
> process can't be preempted for other reasons. KVM uses preempt_count() to check if preemptions is allowed and schedule other process if possible. This works
> with preemptable kernels since they maintain accurate information about
> preemptability in preempt_count. This patch make non-preemptable kernel
> maintain accurate information in preempt_count too.

I'm thinking you're going to have to convince some people this won't
slow them down for no good.

Personally I always have PREEMPT=y, but other people seem to feel
strongly about not doing so.

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