Message-ID: <4E019353.6030902@fusionio.com>
Date: Wed, 22 Jun 2011 09:01:39 +0200
From: Jens Axboe <jaxboe@fusionio.com>
MIME-Version: 1.0
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
        Tejun Heo <tj@kernel.org>
Subject: Re: [RFC][PATCH 1/3] sched, block: Move unplug
References: <20110621233444.094372367@chello.nl> <20110621233648.806475812@chello.nl>
In-Reply-To: <20110621233648.806475812@chello.nl>
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1128
Lines: 27

On 2011-06-22 01:34, Peter Zijlstra wrote:
> Thomas found that we're doing a horrendous amount of work in that scheduler
> unplug hook while having preempt and IRQs disabled.
> 
> Move it to the head of schedule() where both preemption and IRQs are enabled
> such that we don't get these silly long IRQ/preempt disable times.
> 
> This allows us to remove a lot of special magic in the unplug path,
> simplifying that code as a bonus.

The major change here is moving the queue running inline, instead of
punting to a thread. The worry is/was that we risk blowing the stack if
something ends up blocking inadvertently further down the call path.
Since it's the unlikely way to unplug, a bit of latency was acceptable
to prevent this problem.

I'm curious why you made that change? It seems orthogonal to the change
you are actually describing in the commit message.

-- 
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/