linux-kernel - Re: [PATCH 1/2] Avoid bio

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Message-ID: <20080702090048.2ec99b72@lxorguk.ukuu.org.uk>
Date:	Wed, 2 Jul 2008 09:00:48 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	Neil Brown <neilb@...e.de>
Subject: Re: [PATCH 1/2] Avoid bio_endio recursion

On Wed, 2 Jul 2008 00:09:22 -0400 (EDT)
Mikulas Patocka <mpatocka@...hat.com> wrote:

> > Right, that wont work of course. Completions are typically done through
> > a softirq, so it is not currently done with hard interrupts disabled.
> 
> I thought, from hardirq - that's what IDE is doing. And they are called 

Even IDE will sometimes complete from a timer on an error.

> And does local_irq_restore() need to execute even more costy "popf" when 
> it makes a transition from disabled to disabled state? What's 
> local_irq_restore semantics --- is it allowed to use local_irq_restore for 
> transition from interrupt-enabled state into interrupt-disabled state?

If you are worried about performance the network layer has _irq variants
of various functions that are faster and can only be called from the
right context (eg kfree_skb_irq), so you could do two versions of that
code.

Alan
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