Justin Piszcz wrote:

# echo 3 > /proc/sys/vm/drop_caches
# dd if=/dev/md3 of=/dev/null bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 399.352 seconds, 26.9 MB/s
# for i in sde sdg sdi sdk; do   echo 192 > 
/sys/block/"$i"/queue/max_sectors_kb;   echo "Set 
/sys/block/"$i"/queue/max_sectors_kb to 192kb"; done
Set /sys/block/sde/queue/max_sectors_kb to 192kb
Set /sys/block/sdg/queue/max_sectors_kb to 192kb
Set /sys/block/sdi/queue/max_sectors_kb to 192kb
Set /sys/block/sdk/queue/max_sectors_kb to 192kb
# echo 3 > /proc/sys/vm/drop_caches
# dd if=/dev/md3 of=/dev/null bs=1M count=10240 
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 398.069 seconds, 27.0 MB/s

Awful performance with your numbers/drop_caches settings.. !

What were your tests designed to show?
  

To start, I expect then to show change in write, not read... and IIRC (I 
didn't look it up) drop_caches just flushes the caches so you start with 
known memory contents, none.

Justin.

On Fri, 12 Jan 2007, Justin Piszcz wrote:

  

quoted

On Fri, 12 Jan 2007, Al Boldi wrote:

    

quoted

Justin Piszcz wrote:
      

quoted

RAID 5 TWEAKED: 1:06.41 elapsed @ 60% CPU

This should be 1:14 not 1:06(was with a similarly sized file but not the
same) the 1:14 is the same file as used with the other benchmarks.  and to
get that I used 256mb read-ahead and 16384 stripe size ++ 128
max_sectors_kb (same size as my sw raid5 chunk size)
        

max_sectors_kb is probably your key. On my system I get twice the read 
performance by just reducing max_sectors_kb from default 512 to 192.

Can you do a fresh reboot to shell and then:
$ cat /sys/block/hda/queue/*
$ cat /proc/meminfo
$ echo 3 > /proc/sys/vm/drop_caches
$ dd if=/dev/hda of=/dev/null bs=1M count=10240
$ echo 192 > /sys/block/hda/queue/max_sectors_kb
$ echo 3 > /proc/sys/vm/drop_caches
$ dd if=/dev/hda of=/dev/null bs=1M count=10240

      

-- 
bill davidsen [off-list ref]
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979