[PATCH/RFC] readahead applet
Michael Opdenacker
michael-lists at free-electrons.com
Mon Aug 21 18:44:34 UTC 2006
Paul Fox wrote:
> >
> > With our new "readahead" command, everything is done in one system call.
> > So, almost everything is done in kernel mode, possibly in an optimized
> > way between the filesystem and page cache. And of course, no buffer copy
> > from kernel-space to user-space is done!
> >
> > To prove this I ran "time readahead" and "time cat" on 2 identical files.
>
> what's the result if you compare with "time dd bs=<some large number>" ?
>
Here it is:
time dd if=file of=/dev/null bs=40M count=1 (my file is 40M big... it's
the latest kernel sources)
real 0m1.610s
user 0m0.012s
sys 0m0.188s
time dd if=file of=/dev/null bs=1M count=40
real 0m1.774s
user 0m0.016s
sys 0m0.084s
What I had before:
time cat file-copy > /dev/null
real 0m1.485s
user 0m0.012s
sys 0m0.080s
time readahead file
real 0m1.375s
user 0m0.000s
sys 0m0.028s
:-)
Michael.
--
Michael Opdenacker, Free Electrons
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