Re: READAHEAD

[Voluspa]

On 2003-11-01 9:15:28 Age Huisman wrote:
>Andrew Morton wrote:
>> Andrew Morton <akpm@xxxxxxxx> 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
[...]
>Here are the new test results.
[...]
>I think you were right  :-)

I see an improvement with 512 instead of the default 256, but no further
speedups with 1024 or 2048 - no point in trying 4096:

readahead = 256 (on)
real    0m39.494s
user    0m0.346s
sys     0m5.436s
Timing buffered disk reads:  64 MB in  2.80 seconds = 22.84 MB/sec

readahead = 512 (on)
real    0m34.418s
user    0m0.302s
sys     0m5.304s
Timing buffered disk reads:  64 MB in  2.16 seconds = 29.63 MB/sec

And for the nostalgic people out there, here's what "hdparm /dev/hdX"
has in its readahead slot under 2.5.X:

2.5.5-pre1
readahead = 8 (on)

2.5.5-pre1-final (AKA 2.5.5) to 2.5.8-pre2
BLKRAGET failed: Input/output error

2.5.8-pre3 to 2.5.9 don't compile.

2.5.10
readahead = 0 (off)

2.5.11 failed to boot and damaged the filesystem.

2.5.12 and onwards
readahead = 256 (on)

Mvh
Mats Johannesson
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