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

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Date:	Mon, 2 Mar 2009 10:54:35 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Vadim Lobanov <vlobanov@...akeasy.net>
cc:	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

On Mon, 2 Mar 2009, Vadim Lobanov wrote:

> On Monday 02 March 2009 09:11:54 Linus Torvalds wrote:
> > The thing is, with PIO, a 512-byte disk read ends up doing 256 16-bit word
> > reads from the controller, each potentially up to 600ns long (PIO0
> > timings). That's 150ms - for a single sector!
> 
> Out of curiosity, the peanut gallery wishes to ask:
> Is the above supposed to be 600us (*1000), or 150us (/1000)? Probably the 
> latter.

Sorry, I was off by a lot. Yes. /1000. The end result ends up being lots 
better (and I should have realized I did my conversion wrong, because the 
times ended up being _so_ big), but not better enough - we've had dropped 
timer interrupts etc on those kinds of machines unless you use "hdparm -u1".

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).

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. 

			Linus
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