linux-kernel - Re: What's in libata-dev.git

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Message-ID: <20060911153706.GE4955@suse.de>
Date:	Mon, 11 Sep 2006 17:37:06 +0200
From:	Jens Axboe <axboe@...e.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Jeff Garzik <jeff@...zik.org>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...l.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: What's in libata-dev.git

On Mon, Sep 11 2006, Alan Cox wrote:
> Ar Llu, 2006-09-11 am 10:44 -0400, ysgrifennodd Jeff Garzik:
> > > drivers/ide. You might want to do 256 for SATA Jeff but please don't do
> > > 256 for PATA. Reading specs is too hard for some people ;)
> > > 
> > > Some drives abort the xfer, some just choked.
> > 
> > Where in drivers/ide is it limited to 255?
> 
> Being a sensible sanity check it was removed, and that was a small
> mistake. Some 2.4 also has a 256 limit and it broken various transparent
> raid units, older Maxtors(1Gb or so), some IBM drives etc. Got fixed in
> -ac but never in base.
> 
> The failure pattern is pretty ugly too, your box runs and runs and
> eventually you get a linear 256 sector I/O and it all blows up,
> sometimes. The IBM's abort the xfer but the maxtors may or may not get
> it right (its as if half the firmware has the right test).

So this is a confirmed, broken case? Why has no one complained for 2.4
and 2.6?

> We could perhaps do it by ATA version - 255 for ATA < 3 256 for ATA 3+,

Might be sane, yep.

> lots for LBA48 ? Thats assuming you can show 256 sectors is faster than
> 255. I'd bet for normal I/O its unmeasurably small.

255 isn't faster than 256, measurably. But the alignment for "natural"
transfer sizes is much nicer with 256, that's the problem. You really
don't want 248 + 8 going down all the time, for instance. Perhaps it's
not a real problem, but it could be.

-- 
Jens Axboe

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