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CD-writing: buffer underruns writing from HD at 8x writing speed with kernel 2.4.18



Hi,

There once was a time I could copy CDs on the fly, or write them from HD
with 12x (as much as my CDRW supports) without a problem.
Months ago it stopped to work at reasonable speeds. I didn't have the
time to investigate it fully then, unfortunately. Now I did, and here's
the result:

The setup:
kernel is 2.4.18 (I use the low latency patch, but I have tested it
without the patch too, same result)
RW-drive is an IDE Philips CDRW 1208 (cdrdao driver generic-mmc-raw)
ROM-drive is a Plextor PCX-40TS (40x) SCSI drive on an Adaptec
controller (PCI, 2140 IIRC).
Everything is setup ok AFAICS, done according to cd-writing-howto
I use a ~3 yrs old 10 gig IDE HD (the same one I used when everything
went OK), set with hdparm to:
sonic:~# hdparm /dev/hda
/dev/hda:
 multcount    = 16 (on)
 I/O support  =  3 (32-bit w/sync)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 nowerr       =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 1650/255/63, sectors = 26520480, start = 0
 busstate     =  1 (on)
sonic:~#

The PC is an AMD K6 450, IDE chipset is ALI M15x3

There are 2, possibly connected, problems:
1) When I read data from HD I can write ok, as long as the speed doesn't
exceed 8x. Otherwise, I get buffer underruns very soon. gtoaster reports
~1500 kB sustended throughput. There is clearly something wrong. The
cdrdao command line is:
cdrdao --simulate --paranoia-mode 3 --speed 8 --device 1,0,0 --driver
generic-mmc-raw:0x0 --buffers 60

2) When copying on-the-fly, I have to use speeds not exceeding 4x. At
4x, the buffer is always full. At 8x, instant underrun. This may be a
flaky source drive, but in conjunction with the above prob I am not
sure.

I'd be glad if someone could give hints, this drives me crazy.
Thanks, M




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