Re: [patch]: ide dma timeout retry in pio

[James Turinsky]

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