On Thu, 4 Dec 2003 06:28:26 -0600, nate at refried.org wrote:
> On Thu, Dec 04, 2003 at 12:06:09AM -0600, Ian Stoner wrote:
> > After I copy a large file (~30 megs) my processor activity shoots up
> > to 100% for 10 to 15 seconds, and I can't use my system during that
> > time. 
> 
> Sounds like write caching without DMA enabled.  Use hdparm to make
> sure that DMA is enabled on your drives.

That nailed it!  Thanks, Nate.  I had never heard of hdparm--I found a
webpage that recommended some likely safe settings, tried them, and got
a more than 5-fold increase in buffered disc reads.  I've included the
output of the commands I ran, in case anyone cares.  Maybe I'm the only
one who's never heard of hdparm?  If anyone knows of any other
parameters I should pay attention to, please advise.

Thanks again!

root at goodmanbrown:~# hdparm /dev/hda
 
/dev/hda:
 multcount    =  0 (off)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  0 (off)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 2495/255/63, sectors = 40088160, start = 0

root at goodmanbrown:~# hdparm -Tt /dev/hda
 
/dev/hda:
 Timing buffer-cache reads:   368 MB in  2.01 seconds = 183.08 MB/sec
 Timing buffered disk reads:   12 MB in  3.07 seconds =   3.91 MB/sec

root at goodmanbrown:~# hdparm -X66 -d1 -u1 -m16 -c3 /dev/hda
 
/dev/hda:
 setting 32-bit IO_support flag to 3
 setting multcount to 16
 setting unmaskirq to 1 (on)
 setting using_dma to 1 (on)
 setting xfermode to 66 (UltraDMA mode2)
 multcount    = 16 (on)
 IO_support   =  3 (32-bit w/sync)
 unmaskirq    =  1 (on)
 using_dma    =  1 (on)

root at goodmanbrown:~# hdparm -Tt /dev/hda
 
/dev/hda:
 Timing buffer-cache reads:   376 MB in  2.02 seconds = 186.14 MB/sec
 Timing buffered disk reads:   64 MB in  3.04 seconds =  21.05 MB/sec

-- 
Ian Stoner
Philosophy Department
University of Minnesota

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