Use of floating point on typical mailserver

[Greg Matthews]

Jeff A. Earickson wrote:
> Some quick thoughts here.  Search the source code that you compile (eg, 
> sendmail code) for uses of "float", "double", or "math.h" (math lib):
> 
> find . -name '*.[ch]' -print | xargs egrep 'math|float|double'
> 
> I didn't find much in sendmail 8.13.8 source code.  Examine the dynamic 
> libraries that you use with ldd and look for libm (mathlib).  Do an lsof
> as root and look to see if libm is in use by anything.  These quick checks
> on my mail server didn't show much.  Mathlib tends to be the heavy hitter
> for floating-point, since it has trig/log functions and the like in it.

ah.. good suggestions, I'll have a poke around.

> The idea with threads/processes is that the current Niagara chips can run
> 4 threads per CPU.  If the ratio of threads to processes is high, then
> you can keep the CPU busy with threads.  If the ratio is low, then you are
> wasting your money on the CoolThreads CPUs, because you can't keep them 
> busy.  Buy regular Sparc chips instead.

perhaps I'm misunderstanding the technology. Yes each core can execute 
four threads "at once" (actually time sliced) but I dont see that 
there's much difference here between running 8 processes each with 4 
threads or running 32 processes. Each core should still be able to 
context switch between the four processes in its 4 "run queues" whether 
they are threads of a process or separate processes, no? Or is the 
context switch between separate processes much more expensive?

GREG

> 
> Jeff Earickson
> Colby College


-- 
Greg Matthews           01491 692445
Head of UNIX/Linux, iTSS Wallingford

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