linux-kernel - Re: [PATCH 0/2] libata: implement 32-bit transfers for PIO mode

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Message-ID: <20080217230800.GA15374@1wt.eu>
Date:	Mon, 18 Feb 2008 00:08:00 +0100
From:	Willy Tarreau <w@....eu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	jeff@...zik.org, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] libata: implement 32-bit transfers for PIO mode

On Sun, Feb 17, 2008 at 10:31:34PM +0000, Alan Cox wrote:
> > Thus, I have implemented the 32-bit mode to bring the performance back
> > to the level of the old IDE driver. I jumped from 1.5 MB/s to 2.5 MB/s,
> > which is an important difference at this level of performance, especially
> > when large files are read. The 32-bit mode is enabled using the ioctl
> > which is already implemented but only accepts a null value.
> 
> Excellent, that has been on my TODO list for some time and I'd only
> gotten as far as putting into the ISA/VLB drivers rather than generally
> testing.
> 
> I'm not however sure this should be a DFLAG but should be an alernative
> ata_data_xfer method - I say that because VLB needs to wrap it and some
> controllers have quirky rules for 32bit xfers. (Also some small number of
> pre ATA disks can't handle the different timing cycles from a 32bit ISA
> I/O being redirected their way).

Do you think this can cause any trouble considering that default setting
is not changed ? However, I agree that an alternative ata_data_xfer may
make it easier to always enable it on some controllers. Or maybe we should
keep it that way (since this function checks the ioctl value) and add a
pure 32-bit function for 32-bit enabled controllers ? I would say I have
no idea, it's clearly not my domain of expertise :-/

> Alan

Willy

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