----- Original Message -----
From: "Alan Cox" <[EMAIL PROTECTED]>
To: "Mark Hahn" <[EMAIL PROTECTED]>
Cc: "Jens Axboe" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>;
<[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
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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