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

Alexey Popov lol at chistydom.ru
Tue Nov 20 03:57:04 PST 2007


Ivan Voras wrote:
> 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?
There's almost no disk load except writing ~15 strings per second to 
logs. All PHP code fits in memory and there's no need to read disk. 
atime turned off. NFS is not used.

> 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.
I did'nt change CPU myself, but I think this 4-core and 8-core servers 
(Intel SR1500 platform) are different only in CPUs. You can see it in 
dmesg in the root of this thread.

> 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.
Thank you.
I need some time to try all this. I'll report if find something.

With best regards,
Alexey Popov

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