Re: bad lmbench numbers for mmap

V Ganesh (ganesh@vxindia.veritas.com)
Sat, 17 Apr 1999 04:59:30 +0530 (IST)


> From: David Miller <davem@twiddle.net>
> From: V Ganesh <ganesh@vxindia.veritas.com>
>
> I just posted the raw numbers and we are roughly twice as slow as
> solaris.
>
> At least it is consistant with the fact that the solaris run had to
> touch roughly half as much memory during the benchmark than Linux did.

not really, unless I'm really mistaken.
lat_mmap's man page says:
...
The benchmark maps in and unmaps the first size bytes of
the file repeatedly and reports the average time for one
mapping/unmapping.
...
Output format is "%0.2f %d\n", megabytes, usecs, i.e.,
8.00 1200

so from the raw output for linux's lat_mmap run, we get stuff like
16.777216 17745
33.554432 35039
and from solaris, we get
16.777216 9321

of course we can't use the 32M mmap on linux for comparison (which is
what I mistakenly did at first), but surely we can compare the two
16 meg mmaps ? and solaris is definitely consistently faster by a factor
of roughly 2. total memory size is irrelevant unless you directly (and wrongly)
compare the "make see" output of machines which don't have identical
amts of RAM.

ganesh

ganesh

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