Messages in this thread | | | Date | Sun, 2 Nov 2003 18:15:56 -0600 (CST) | From | Derek Foreman <> | Subject | Re: READAHEAD |
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On Fri, 31 Oct 2003, Andrew Morton wrote:
> Andrew Morton <akpm@osdl.org> wrote: > > > > Please, just use time, cat, dd, etc. > > > > mount /dev/xxx /mnt/yyy > > dd if=/dev/zero of=/mnt/yyy/x bs=1M count=1024 > > umount /dev/xxx > > mount /dev/xxx /mnt/yyy > > time cat /mnt/yyy/x > /dev/null > > And you can do the same against /dev/hdaN if you have a scratch > partition; that would be interesting.
I don't have a scratch partition, but the effect is quite apparent when reading from /dev/hd*
I have 384 megs of ram, no swap, and echo 0 > /proc/sys/vm/swappiness kernel is 2.6.0-test9
hdparm -qa 0 /dev/hde ; dd if=/dev/hde of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes transferred in 103.038178 seconds (10420815 bytes/sec)
hdparm -qa 128 /dev/hde ; dd if=/dev/hde of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes transferred in 34.171719 seconds (31421943 bytes/sec)
hdparm -qa 256 /dev/hde ; dd if=/dev/hde of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes transferred in 34.994348 seconds (30683293 bytes/sec)
hdparm -qa 4096 /dev/hde ; dd if=/dev/hde of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes transferred in 22.268371 seconds (48218247 bytes/sec)
(hdparm -t /dev/hde opens /dev/hde and reads it for a few seconds, so these numbers are much the same as my hdparm -t scores)
I also get similar results from /dev/md0 in another machine (the only not-ide device I can test on... but it's still a bunch of ide drives).
note... For people playing with hdparm, hdparm -a 123 -t /dev/drive doesn't set the readahead before running the test. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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