dd test discussion (was Re: possible regression?)

[Mulyadi Santosa]

On Fri, Jan 21, 2011 at 20:25, Mag Gam <magawake at gmail.com> wrote:
> Typo, in Box 5. Wrong kernel version
>
> Box 5, RHEL 5.4, 2.6.36, dd bs=1024 count=1000000 if=/dev/zero
> bs=4096k of=/dev/null
>
> Anyone had a chance to try this? :-)

$ for a in `seq 1 3`; do \time dd bs=4K count=1M if=/dev/zero of=/dev/null; done

1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB) copied, 1.38893 seconds, 3.1 GB/s
0.21user 1.17system 0:01.39elapsed 99%CPU (0avgtext+0avgdata 2768maxresident)k
0inputs+0outputs (0major+209minor)pagefaults 0swaps

1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB) copied, 1.39358 seconds, 3.1 GB/s
0.23user 1.16system 0:01.39elapsed 99%CPU (0avgtext+0avgdata 2768maxresident)k
0inputs+0outputs (0major+209minor)pagefaults 0swaps


1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB) copied, 1.4527 seconds, 3.0 GB/s
0.17user 1.23system 0:01.45elapsed 96%CPU (0avgtext+0avgdata 2752maxresident)k
0inputs+0outputs (0major+208minor)pagefaults 0swaps


I slightly modified your dd test. Again, this is on 2.6.36.

IMO, you shouldn't worry much about it. Were experiencing something
that related to memory access? It's not a NUMA box, right? Or are you
using PAE? just capping into 896 MB maybe? non standart VM split other
than 3:1?

PS: I rewrite the subject to better match the discussion. With the
hope readers well get better understanding about what the discussion
is all about. Hope you don't mind....

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com