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SubjectRe: [patch]: ide dma timeout retry in pio
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----- Original Message -----
From: "Alan Cox" <alan@lxorguk.ukuu.org.uk>
To: "Mark Hahn" <hahn@coffee.psychology.mcmaster.ca>
Cc: "Jens Axboe" <axboe@suse.de>; <andre@linux-ide.org>;
<alan@lxorguk.ukuu.org.uk>; <linux-kernel@vger.kernel.org>
Sent: Monday, May 28, 2001 5:12 PM
Subject: Re: [patch]: ide dma timeout retry in pio

> > really? do we know the nature of the DMA engine problem well
enough?
>
> I can categorise some of them:
>
> 1. Hardware that just doesnt support it.
> 2. Timeouts that are false positives caused by disks having problems
> and being very slow to recover
> 3. Bad cabling
> 4. Stalls caused by heavy PCI traffic
>
> > is there a reason to believe that it'll work better "later"?
>
> #1 will go fail, fail, fail -> PIO now (or should do Im about to try
it)
> #2 and #4 will be transient
> #3 could go either way


Where does the "'DMA Timeout -> disable DMA' then lose all
responsiveness when I issue 'hdparm -d1' while it tries and fails to
re-enable DMA" fit in? The disk will happily run for several days in
UDMA33 and then at some point it craps out with a DMA timeout which
results 1) DMA being turned off and 2) all attempts to re-enable DMA
failing?

And what's up with this:

[root@MoveAlong james]# hdparm /dev/hda

/dev/hda:
multcount = 0 (off)
I/O support = 1 (32-bit)
unmaskirq = 1 (on)
using_dma = 1 (on)
keepsettings = 1 (on)
nowerr = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 19590/16/63, sectors = 19746720, start = 0
[root@MoveAlong james]# hdparm -tT /dev/hda

/dev/hda:
Timing buffer-cache reads: 128 MB in 6.98 seconds = 18.34 MB/sec
Timing buffered disk reads: 64 MB in 5.77 seconds = 11.09 MB/sec
Hmm.. suspicious results: probably not enough free memory for a proper
test.
[root@MoveAlong james]# free
total used free shared buffers
cached
Mem: 126800 123460 3340 0 67284
41572
-/+ buffers/cache: 14604 112196
Swap: 394624 32816 361808

I used to get ~33MB/sec on buffer-cache and ~10MB/sec on buffered disk
reads in 2.2...

--JT

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