2 x quad-core system is slower that 2 x dual core on FreeBSD

Ivan Voras ivoras at freebsd.org
Mon Nov 19 10:35:33 PST 2007

Alexey Popov wrote:

> Here is it:

I don't see anything unusual there.

Some more ideas: How is your disk load (iostat, systat -vm, diskinfo -t)
during the load? You don't use NFS for the web directories, do you?

Can you run bonnie++ while the machine is idle (i.e. apache is stopped)
just to verify it isn't a stupid problem with the disks or the driver?

>> Also, did you try configuring and running pecl-APC for PHP?'s
> I'm using eAccelerator. Again, the same soft works good on less-CPU
> system and on Linux.

So, you pick the CPU out of the motherboard and plug in another one? If
not, you can't be sure that some other thing isn't wrong. I know you
tried it on Linux, but it might use slightly different commands in the
driver that don't trigger the error. I'm very surprised that both 6.x
and 7.x behave almost the same on your load: since they are very
different in how they support multiple CPU-s, I'd expect a big
difference in this case (in favour of 7.x), not a small one. This might
point that the problem is not in the OS itself, but maybe in the
hardware or in some driver.

Many people (including me) have run FreeBSD on machines like yours
without such problems, so let's dig further.

You don't have WITNESS, INVARIANTS, DIAGNOSTICS or something similar
enabled? Can you try a generic SMP kernel (called "SMP" in 6.x; the
"GENERIC" in 7.x has SMP by default) and see how it works?

Can you disable SMP and try with only one CPU (on the 2xquad machine)?
You can do it in loader.conf by setting kern.smp.disabled=1, or perhaps
in BIOS. If there's a problem in some hardware or a driver, you'd still
get a big load on sys time. You might also want to halt certain logical
CPUs in the OS itself (see smp(4) man page) and see if there's a certain
relationship between how many CPUs are running and what the sys load is.

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