Re: Q: why _less_ performance on machine with SMP then with UP kernel ?

[Andrew Walrond <andrew@walrond.org>]

On Tuesday 13 September 2005 22:12, Danny ter Haar wrote:
>
> From yesterday till 10:30am i ran 2.6.13.1 in UP mode.
> As you can see blue (==incoming traffic) is fairly constant.
> This morning i compiled/installed 2.6.14-rc1-smp.
> I let it ran till 12:15 but it's clear that it can't keep up
> with the flow of data. I rebooted to 2.6.14-rc1 (UP) and that
> keeps up with the data just fine.
>
> So what is the difference between UP & SMP ?

Is there any indication in the system log that your userland (news?) software 
was having problems? It may be entirely unrelated to your problem, but you 
should anyway be aware of a nasty unresolved issue with all smp kernels >=  
2.6.12 on smp x86_64 systems:

	http://bugzilla.kernel.org/show_bug.cgi?id=4851

If you have any indication of userland problems, you might try
	echo 0 > /proc/sys/kernel/randomize_va_space
which much reduces (but seemingly does not completely remove) this issue for 
most people.

>
> A very confused
>

One of the major symptoms of this particular bug ;)

Andrew Walrond
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