On Mon, Jan 29, 2001 at 12:06:01PM -0500, Larry Marshall wrote:
> > I found out a few months ago that Linux takes a default stance
> > of not enabling DMA on the IDE controllers. This lowers disk
> > throughput a lot. For
>
> Hmmm...would you know if that's the change that's taken place between
> v7.1 and v7.2 of Mandrake (2.2.15 -> 2.2.17 kernel)? I had no streams
> problems with any version of Linux prior to LM7.2 but it's real enough
> with it.
There are some kernel compiliation options which affect this, but I
think they have been around for a while (I always compile my own
kernels anyway). I don't know what Mandrake compiles into their
default kernels, but if they provide a copy of the configuration, you
can grep for "DMA" to see if it is enabled. Here is what the help text
says for 2.2.17:
CONFIG_BLK_DEV_IDEDMA
If your PCI system uses IDE drive(s) (as opposed to SCSI, say) and
is capable of bus-master DMA operation (most Pentium PCI systems),
you will want to say Y here to reduce CPU overhead. You can then use
the "hdparm" utility to enable DMA for drives for which it was not
enabled automatically. By default, DMA is not enabled automatically
for these drives, but you can change that by saying Y to the
following question "Use DMA by default when available". You can get
the latest version of the hdparm utility via anonymous FTP from
ftp://metalab.unc.edu/pub/Linux/system/hardware/.
CONFIG_IDEDMA_AUTO
Prior to kernel version 2.1.112, Linux used to automatically use
DMA for IDE drives and chipsets which support it. Due to concerns
about a couple of cases where buggy hardware may have caused damage,
the default is now to NOT use DMA automatically. To revert to the
previous behaviour, say Y to this question.
If you suspect your hardware is at all flakey, say N here.
Do NOT email the IDE kernel people regarding this issue!
It is normally safe to answer Y to this question unless your
motherboard uses a VIA VP2 chipset, in which case you should say N.
Bob
--
Bob Nielsen, N7XY [EMAIL PROTECTED]
Bainbridge Island, WA http://www.oz.net/~nielsen
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