different behaviour between 4.x and 5.x (ping response/disk io) [was Re: ]

stheg olloydson stheg_olloydson at yahoo.com
Sun Jan 16 16:42:57 PST 2005

(Sorry about the multiple posts. I somehow sent this without a subject
line before.)

it was said:

>Now i am really puzzled because i cannot understand why 4.x behaves 
>relatively good compared to 5.x on this specific issue. Is there a
>good explanation or does one have to investigate this further?


First, I do not speak for anyone but myself. Therefore, any information
this post contains is based solely on my understanding of that
information and is only as accurate as that understanding is correct.

To sum up your problem, you tested "FreeBSD 5.3, NetBSD 2.0, FreeBSD
4.11 and an elder version of the Knoppix (Linux 2.4) CD" and found that
FreeBSD 4.11RC2 had the best ping responses from that group. What you
want to know is why FBSD 5.3 doesn't respond as well as 4.11RC2. Is
this correct?
Assuming that it is, the answer is that 5.3 is the first stable release
of the 5.x branch. One of the 5.x branch's main purposes is to make
FBSD much more scalable in terms SMP support. Doing this requires
removing the Giant lock. It had been hoped that the removal process
would be finished in time for 5.3. Unfortunately, as often happens in a
volunteer project delays occurred for various reasons, that was not the
case. The incomplete removal meant that not all subsystems could be
optimized properly. One of those subsystems is networking.
This is not as bad as it sounds because while 5.3's network performance
is not as good as 4.11RC2, it is no worse that of NBSD 2.0 or any Linux
distro. Also, the optimization has already begun on networking and 5.4
should be _at least_ as good as 4.x.
Also, as you saw yourself, using an SMP kernel in FBSD 5.3 doesn't
cause a performance hit in networking but it does in NBSD 2.0.
So your choices seem to be use 4.11RC2 (full release due shortly) to
get the best network response, 5.3 to get as good performance as NBSD
2.0 but with SMP, or use NBSD 2.0 to get as good perfomance as 5.3 but
without SMP. Of course, you can wait until NBSD (your prefered OS)
performs as well as FBSD, but that may be a loooonng time.:)



P.S. (to the list in general) Why do all of the questions about FBSD
performance, especially 4.x vs 5.x, come from people posting from
Windows boxes? Theories?

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