Hi.
Tom Evans wrote:
After that I rebuilt with SMP GENERIC kernel and put on that server 2
times more requests that UP could handle. For the first time it worked
good. Then I increased load to 2.5 times more than UP. Immediately
Apache child count increased to MaxClients (24), most of them in RUN
state, and %sys became greater than %user (see attach). I think after
some threshold of load FreeBSD is paying more CPU time to the management
of running processes than to run them.
MaxClients of 24 seems very low for a 8 cpu box, running prefork MPM. On
our quad CPU boxes, running custom apache modules, we use
MaxClients 70
MinSpareServers 5
MaxSpareServers 15
StartServers 20
Perhaps you are seeing high system load because the system is having to
maintain a lot of queued connections. Certainly, our load remains
in-between comfortable margins, except when heavily stressed.
I believe 8-core FreeBSD server is able to maintain 1024 waiting TCP
connections without measurable CPU load.
As of this problem: increasing MaxClients leads to growing %sys part of
CPU load. Generally large MaxClients value is useful when most Apache
children are waiting for I/O or something else but CPU.
With best regards,
Alexey Popov
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