From: Stephen Hemminger <shemminger@osdl.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org
Subject: Re: [RFC 1/2] irq: record edge-level setting
Date: Mon, 24 Apr 2006 15:58:12 -0700 [thread overview]
Message-ID: <20060424155812.68d45cb1@localhost.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.64.0604241527060.3701@g5.osdl.org>
On Mon, 24 Apr 2006 15:34:20 -0700 (PDT)
Linus Torvalds <torvalds@osdl.org> wrote:
>
>
> On Mon, 24 Apr 2006, Stephen Hemminger wrote:
> >
> > Maybe that's why it never was done in the past, too much work and historical
> > baggage.
>
> It's messy. That whole ELCR register was mis-designed: you can change the
> edge/level detection with it, but since it _also_ changes the polarity of
> the signal, you can't actually do so from a sw angle, and it has to match
> the hardware. So you can't say "I want to treat this interrupt as level
> triggered", and just set the bit ;^/
>
> To make matters worse, I wouldn't be in the least surprised if the ELCR
> register is totally ignored by many south-bridges for the internally
> generated interrupts (ie devices that are embedded in the SB), since the
> register really doesn't matter for them.
>
> And it doesn't help that Intel mis-designed the edge-detection logic on
> the IO-APIC. On the old i8259, if you masked an interrupt and unmasked it,
> an active interrupt would always be seen as an edge, because the
> edge-detection was done _after_ masking. On the IO-APIC crap, the masking
> is done after edge-detection, so if you mask the APIC hardware level, and
> an edge happens, you'll never ever learn of it ever again.
That is the kind of crap that makes NAPI difficult.
See Documentation/networking/NAPI_HOWTO.txt for rotting packet..
> I'm sure other system architectures have similar problems, but it's
> irritating.
>
> Linus
next prev parent reply other threads:[~2006-04-24 22:58 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-24 18:41 better leve triggered IRQ management needed Stephen Hemminger
2006-04-24 18:59 ` linux-os (Dick Johnson)
2006-04-24 19:02 ` Linus Torvalds
2006-04-24 19:08 ` Linus Torvalds
2006-04-24 19:53 ` Arjan van de Ven
2006-04-24 20:16 ` Alan Cox
2006-04-24 20:43 ` Arjan van de Ven
2006-04-24 21:07 ` Linus Torvalds
2006-04-24 21:20 ` Alan Cox
2006-04-24 22:26 ` Linus Torvalds
2006-04-24 21:22 ` [RFC 1/2] irq: record edge-level setting Stephen Hemminger
2006-04-24 21:49 ` Alan Cox
2006-04-24 21:41 ` Stephen Hemminger
2006-04-24 22:34 ` Linus Torvalds
2006-04-24 22:58 ` Stephen Hemminger [this message]
[not found] ` <20060424141926.3872f921@localhost.localdomain>
2006-04-24 21:22 ` [RFC 2/2] warn on shared edge-triggered irq Stephen Hemminger
2006-04-25 15:23 ` better leve triggered IRQ management needed Michael Buesch
2006-04-24 19:15 ` Russell King
2006-04-24 20:18 ` Linus Torvalds
2006-04-24 19:25 ` Stephen Hemminger
2006-04-24 19:35 ` linux-os (Dick Johnson)
2006-04-24 20:19 ` Linus Torvalds
2006-04-24 20:50 ` linux-os (Dick Johnson)
2006-04-24 21:09 ` Linus Torvalds
2006-04-29 21:25 ` Alan Cox
2006-04-29 21:58 ` Linus Torvalds
2006-04-30 4:48 ` Neil Brown
2006-04-30 5:19 ` Linus Torvalds
2006-04-30 6:13 ` Neil Brown
2006-04-30 6:59 ` Linus Torvalds
2006-05-02 5:10 ` Neil Brown
2006-05-02 15:05 ` Linus Torvalds
2006-04-30 7:36 ` Arjan van de Ven
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