possible regression?

[Mag Gam]

I am using RHEL 5.1. Sorry for not being clear.

I wil give this a try today when I go back to class. But I was just
curious why this was happening.  How would one disable "block merge"
efficiency? Has this feature been added recently?

On Thu, Jan 20, 2011 at 12:28 AM, Mulyadi Santosa
<mulyadi.santosa at gmail.com> wrote:
> Hi...
>
> On Thu, Jan 20, 2011 at 10:36, Mag Gam <magawake at gmail.com> wrote:
>> Running on Redhat 5.1 if I do,
>
> Are you sure you're using that archaic distro? Or are you talking
> about RHEL 5.1?
>
>> dd bs=1024 count=1000000 if=/dev/zero of=/dev/null
>>
>> I get around 30Gb/sec
>
> Hm, mine is:
> $ dd bs=1024 count=1000000 if=/dev/zero of=/dev/null
> 1000000+0 records in
> 1000000+0 records out
> 1024000000 bytes (1.0 GB) copied, 1.12169 seconds, 913 MB/s
>
> This is on 2.6.36 SMP kernel compiled with gcc version 4.1.2 20080704
> (Red Hat 4.1.2-48).
>
>>
>> However, when I do this with 2.6.37 I get close to 5GB/sec
>
> what if you use another blocksize, let's say 4K or even 32K? here's
> mine (again):
> $ dd bs=4K count=1000000 if=/dev/zero of=/dev/null
> 1000000+0 records in
> 1000000+0 records out
> 4096000000 bytes (4.1 GB) copied, 1.31167 seconds, 3.1 GB/s
>
> $ dd bs=32K count=1000000 if=/dev/zero of=/dev/null
> 1000000+0 records in
> 1000000+0 records out
> 32768000000 bytes (33 GB) copied, 4.91775 seconds, 6.7 GB/s
>
> see the difference?
>
> IMHO it's a matter of what I call "block merge efficiency"....the more
> you stuff pages (that fits into a "magic" number), the faster I/O you
> got.
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>