Re: IRQF_DISABLED problem
From: Mark Lord
Date: Thu Aug 02 2007 - 11:41:15 EST
Robert Hancock wrote:
David Miller wrote:
From: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
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..
There's another thread on lkml currently about this exact issue,
whereby the UART "fifo nearly full" interrupt isn't getting in quickly
enough for the kernel to de-assert RTS in time..
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