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
next prev parent 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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