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Date: Sun, 20 Jan 2002 10:55:27 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
X-X-Sender: davide@blue1.dev.mcafeelabs.com
To: Jens Axboe <axboe@suse.de>
cc: Andre Hedrick <andre@linuxdiskcert.org>,
        Anton Altaparmakov <aia21@cam.ac.uk>,
        Linus Torvalds <torvalds@transmeta.com>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: Linux 2.5.3-pre1-aia1
In-Reply-To: <20020120114850.J27835@suse.de>
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On Sun, 20 Jan 2002, Jens Axboe wrote:

> On Sat, Jan 19 2002, Andre Hedrick wrote:
> > > On Sat, Jan 19 2002, Andre Hedrick wrote:
> > > > On Sat, 19 Jan 2002, Jens Axboe wrote:
> > > >
> > > > > On Fri, Jan 18 2002, Davide Libenzi wrote:
> > > > > > Guys, instead of requiring an -m8 to every user that is observing this
> > > > > > problem, isn't it better that you limit it inside the driver until things
> > > > > > gets fixed ?
> > > > >
> > > > > There is no -m8 limit, 2.5.3-pre1 + ata253p1-2 patch handles any set
> > > > > multi mode value.
> > > > >
> > > > > --
> > > > > Jens Axboe
> > > > >
> > > >
> > > > And that will generate the [lost interrupt], and I have it fixed at all
> > > > levels too now.
> > >
> > > How so? I don't see the problem.
> >
> > Unlike ATAPI which will generally send you more data than requested on
> > itw own, ATA devices do not like enjoy or play the game.  Additionally the
>
> Unrelated ATAPI fodder :-)
>
> > current code asks for 16 sectors, but we do not do the request copy
> > anymore, and this mean for every 4k of paging we are soliciting for 8k.
>
> The (now) missing copy is unrelated.
>
> > We only read out 4k thus the device has the the next 4k we may be wanting
> > ready.  Look at it as a dirty prefetch, but eventally the drive is going
> > to want to go south, thus [lost interrupt]
>
> Even if the drive is programmed for 16 sectors in multi mode, it still
> must honor lower transfer sizes. The fix I did was not to limit this,
> but rather to only setup transfers for the amount of sectors in the
> first chunk. This is indeed necessary now that we do not have a copy of
> the request to fool around with.
>
> > Basically as the Block maintainer, you pointed out I am restricted to 4k
> > chunking in PIO.  You decided, in the interest of the block glue layer
> > into the driver, to force early end request per Linus's requirements to
> > return back every 4k completed to block regardless of the size of the
> > total data requested.
>
> Correct. The solution I did (which was one of the two I suggested) is
> still the cleanest, IMHO.
>
> > For the above two condition to be properly satisfied, I have to adjust
> > and apply one driver policy make the driver behave and give the desired
> > results.  We should note this will conform with future IDEMA proposals
> > being submitted to the T committees.
>
> I still don't see a description of why this would cause a lost
> interrupt. What is the flaw in my theory and/or code?

Guys, i'm sorry to report you bad news but i still get 'lost interrupt'
with all applied patches ( Anton and Andre ).




- Davide


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