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From: Krzysztof Halasa <khc@pm.waw.pl>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Arjan van de Ven <arjan@infradead.org>,
	"Lennart Baruschka" <FunFlyer@gmx.net>,
	linux-kernel@vger.kernel.org
Subject: Re: Disabling DMA with ICH10?
Date: Wed, 30 Sep 2009 14:21:53 +0200	[thread overview]
Message-ID: <m3hbukfwri.fsf@intrepid.localdomain> (raw)
In-Reply-To: <20090929233505.7ff11cad@lxorguk.ukuu.org.uk> (Alan Cox's message of "Tue, 29 Sep 2009 23:35:05 +0100")

Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

> INB foo
>
> 	CPU -> PCI device		read this register
> 	PCI device -> Disk
> 			trundle whirr whirrr
> 			clunk clunk thud
> 	Disk -> PCI device
> 	PCI device -> CPU... "5"
>
> INB completes
>
> The INB is not interruptible mid instruction and stalls the CPU for the
> full period of the message passing back and forth across the bus. So PIO
> 0 on PCI stalls the bus for the equivalent of an ISA access, and PIO4
> while a good deal faster is still a very long stall in hard real time
> terms.

Sure :-)

That's why I wrote it's a bad idea. I just wanted to correct the
statement about ISA speed - it's not (necessarily) ISA speed, though
it's slow and uses 100% CPU (core) time. (And PIO on PCI* in general
is not much faster, though usually faster than ISA).
-- 
Krzysztof Halasa

  reply	other threads:[~2009-09-30 12:21 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-28 21:31 Disabling DMA with ICH10? Lennart Baruschka
2009-09-28 20:37 ` Alejandro Riveira Fernández
2009-09-28 22:40 ` Alan Cox
2009-09-29  7:54   ` Lennart Baruschka
2009-09-29  8:11     ` Arjan van de Ven
2009-09-29 12:29       ` Krzysztof Halasa
2009-09-29 17:05         ` Alan Cox
2009-09-29 20:35           ` Krzysztof Halasa
2009-09-29 22:35             ` Alan Cox
2009-09-30 12:21               ` Krzysztof Halasa [this message]
2009-09-29 10:46     ` Alan Cox

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