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Very high system load writing data to SCSI DVD-RAM

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Oliver Feiler

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Feb 5, 2001, 1:31:41 PM2/5/01
to linux-...@vger.kernel.org
Hello,

I have the following problem with a DVD-RAM drive. The drive is a
Panasonic LF-D101 connected to a Tekram DC395U SCSI controller. Kernel is
2.2.18 with the patch for the Tekram controller
(http://www.garloff.de/kurt/linux/dc395/).

When I write huge amounts of data to a DVD-RAM the system load is
getting very high, like 10 or even above and the system temporarily freezes
for a short time every minute or so while writing data to the drive. The DVD
drive writes data with 1.35 MB/sec on the discs so there is not really much
data going over the SCSI controller. Reading data from DVD-RAMs is done with
2.7 MB/s (2x) by the drive and does not cause any problems at all.

This problem also existed with previous kernels (2.2.16/17) and with
another SCSI controller I had before the Tekram. Adaptec 2904CD using the
aic7xxx driver.

There is a 4x Teac burner connected to the SCSI controller as well.
Burning CDs does not raise the system load or cause any other problems.

Bye,
Oliver

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Jens Axboe

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Feb 5, 2001, 1:48:01 PM2/5/01
to Oliver Feiler, linux-...@vger.kernel.org
On Mon, Feb 05 2001, Oliver Feiler wrote:
> Hello,
>
> I have the following problem with a DVD-RAM drive. The drive is a
> Panasonic LF-D101 connected to a Tekram DC395U SCSI controller. Kernel is
> 2.2.18 with the patch for the Tekram controller
> (http://www.garloff.de/kurt/linux/dc395/).
>
> When I write huge amounts of data to a DVD-RAM the system load is
> getting very high, like 10 or even above and the system temporarily freezes
> for a short time every minute or so while writing data to the drive. The DVD
> drive writes data with 1.35 MB/sec on the discs so there is not really much

This is an old problem, and not related to the dvd-ram itself. If you
dirty lots of data and the target device is slow, kswapd/bdflush
will go crazy trying to free up memory. It should behave better on
2.4.1, where we impose a global limit on locked buffers. Try and run
a vmstat 1 while doing the copy, and send that along.

> data going over the SCSI controller. Reading data from DVD-RAMs is done with
> 2.7 MB/s (2x) by the drive and does not cause any problems at all.

Reading is much easier to control.

> There is a 4x Teac burner connected to the SCSI controller as well.
> Burning CDs does not raise the system load or cause any other problems.

Burning CDs is very different and does not put pressure on the mm.

--
Jens Axboe

Oliver Feiler

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Feb 6, 2001, 4:24:53 AM2/6/01
to Jens Axboe, linux-...@vger.kernel.org
Jens Axboe wrote:
>
> This is an old problem, and not related to the dvd-ram itself. If you
> dirty lots of data and the target device is slow, kswapd/bdflush
> will go crazy trying to free up memory. It should behave better on
> 2.4.1, where we impose a global limit on locked buffers. Try and run
> a vmstat 1 while doing the copy, and send that along.

Ok, here is it. Started vmstat right before I copied 150 MB to a disc
and let it run until moving the data was finished. The system froze once
during that for about 20 sec and the system load went to about 8.

Hmm, the system has 192 MB RAM if that may be of importance for the
output of vmstat.

Bye

vm
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