Re: [PATCH] readahead: initial method - expected read size - fix fastcall

On Tue, 6 Jun 2006 10:57:28 +0800 Fengguang Wu wrote:
[...]
> Would you test two simple commands by the way?
> 
>         time (find / >/dev/null)
>         (repeat and drop the first result)
> 
>         dd if=/dev/zero of=sparse bs=1M seek=5000 count=1
> 
>         time cp sparse /dev/null
>         (repeat and drop the first result)
> 
> These commands measure the pure cpu(or software) overhead of the
> readahead logics, without ever hitting the physical device. I have
> no 64bit cpu numbers for them yet ;)

The commands don't make sense (I'm in bash)... Also, I refuse to
overwrite /dev/null ;-) I've done a test with "cat" but the first
and second run of it are the same, so it does touch the disk, it seems:

root:sleipner:~# grep setra /etc/rc.d/rc.local
#/sbin/blockdev --setra 2048 /dev/hda
/sbin/blockdev --setra 256 /dev/hda
root:sleipner:~# uname -r
2.6.17-rc5-git10-ar2

root:sleipner:~# time find / >/dev/null

real    3m34.119s
user    0m1.118s
sys     0m5.844s
root:sleipner:~# time find / >/dev/null

real    0m2.949s
user    0m0.691s
sys     0m2.253s
root:sleipner:~# dd if=/dev/zero of=sparse bs=1M seek=5000 count=1
1+0 records in
1+0 records out
root:sleipner:~# time cat sparse >/dev/null

real    0m9.377s
user    0m0.140s
sys     0m8.715s
root:sleipner:~# time cat sparse >/dev/null

real    0m9.593s
user    0m0.138s
sys     0m8.680s
*******************************************************************

root:sleipner:~# grep setra /etc/rc.d/rc.local
/sbin/blockdev --setra 2048 /dev/hda
#/sbin/blockdev --setra 256 /dev/hda
root:sleipner:~# uname -r
2.6.17-rc5-git10-ar2

root:sleipner:~# time find / >/dev/null

real    3m33.037s
user    0m1.112s
sys     0m5.821s
root:sleipner:~# time find / >/dev/null

real    0m2.538s
user    0m0.622s
sys     0m1.911s
root:sleipner:~# dd if=/dev/zero of=sparse bs=1M seek=5000 count=1
1+0 records in
1+0 records out
root:sleipner:~# time cat sparse >/dev/null

real    0m11.279s
user    0m0.163s
sys     0m10.340s
root:sleipner:~# time cat sparse >/dev/null

real    0m11.268s
user    0m0.154s
sys     0m10.412s

Mvh
Mats Johannesson
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