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

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Message-Id: <200903021045.20723.vlobanov@speakeasy.net>
Date:	Mon, 2 Mar 2009 10:45:20 -0800
From:	Vadim Lobanov <vlobanov@...akeasy.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 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.

> For example, Mode2 timings are probably still something we should consider
> realistic, and that's 240ns per word - a single sector now takes ~60ms to
> read off the disk.

Same factor of 1000 question here.

> And we don't do single sectors. Most transfers will be 8 sectors (4k
> contiguos read). So now that 60ms is 480ms per such IDE interrupt. And
> even with the _good_ timings, we're certainly looking at a reduction of
> that to about half.
>
> Imagine what happens when we have interrupts disabled for half a second at
> a time.

-- Vadim Lobanov

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