linux-kernel - Re: IRQF_DISABLED problem

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Date:	Sun, 29 Jul 2007 09:41:04 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	David Miller <davem@...emloft.net>
Cc:	arjan@...radead.org, torvalds@...ux-foundation.org, matthew@....cx,
	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: IRQF_DISABLED problem

David Miller wrote:
> From: Arjan van de Ven <arjan@...radead.org>
> Date: Fri, 27 Jul 2007 13:11:56 -0700
> 
>> On Thu, 2007-07-26 at 16:17 -0700, Linus Torvalds wrote:
>>> On Thu, 26 Jul 2007, Linus Torvalds wrote:
>>>>  (c) "one IRQF_DISABLED means that everything runs disabled". This is 
>>>>      quite possibly buggy.
>>> (Side note: I'm not claiming this (or it's mirror image (d)) is really any 
>>> better/worse than the current behaviour from a theoretical standpoint, but 
>>> at least the current behaviour is _tested_, which makes it better in 
>>> practice. So if we want to change this, I think we want to change it to 
>>> something that is _obviously_ better).
>> my personal preference would actually be to just never enable
>> interrupts. It's the fastest solution obviously, the most friendly on
>> stack and.. well simplest. Drivers no longer need to play some of the
>> games that they do today. And while there is an argument that this may
>> introduce a bit of latency... I'm not really convinced.
> 
> If you have a "chirpy" serial controller with only a 1 byte
> fifo, even a quite reasonable interrupt handler can cause
> receive characters to get lost if you disable interrupts during
> the entirety of it's execution.
> 
> It really is needed.
> 
> And it's just plain rude to disable interrupts when it isn't
> absolutely necessary.

Does anyone really use those serial controllers with no FIFO anymore? 
They've never been reliable for remotely high speeds..

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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