linux-kernel - Re: [RFC][PATCH] irq: remove IRQF

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Date:	Thu, 05 Mar 2009 10:40:44 -0500
From:	Mark Lord <lkml@....ca>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Vadim Lobanov <vlobanov@...akeasy.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] irq: remove IRQF_DISABLED

Linus Torvalds wrote:
>
> Although it porbably does mean that the problem tends to be more in the 
> really bad mode0 case (600ns -> 150us/sector -> milliseconds for 
> multi-sector transfers).
..

Heh.. it's worse that that: even with commonplace mode4 (120ns) transfers,
each PCI bus transaction from start to finish often takes about 1us,
so for a 16-sector multi-sector read, that means 4ms+ with interrupts off.

> I forget what our multi-sector limit is, I think it tends to be 16. So 
> you'll never get _really_ long irq-off times, but "several ms" is still 
> pretty damn bad. 
..

It's a device limit, usually 8 or 16 sectors for nearly all drives now.

Cheers
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