ThreadsPerChild in Apache2 vs THR in top using Event MPM

[Julian Elischer]

craig at animalhead.com wrote:
> This is more of an Apache question than a FreeBSD question, but I've
> received no response from enquiries to the users at httpd list.  Perhaps
> someone receiving from this list will be able to help?
> 
> Our server is running Apache 2.2.11 with the Event MPM under FreeBSD
> 6.3, on a site that's largely mod_perl2 driven.

It depends on which threading library you are using
if you see (in top -H) threads waiting in kserel
tehn you are using the M:N library, where not every thread in the
process makes a kernel thread until it's needed.
if you link with libthr instead (see man libmap)
you may see different results. (and performance)
libthr is the default in 7.x.

> 
> ThreadsPerChild is specified as 25 in an include file of httpd.conf.
> 
> The documentation of the Worker MPM (which is said to have the same
> configuration characteristics as Event) states that each child process
> creates <ThreadsPerChild> threads when it starts, and never changes the
> number of threads.
> 
> But the THR column of the 'top' utility shows 11 threads per process.
> Is 'top' just wrong, or is something constraining how many threads are
> being created?  Might my Internet Hosting Provider have built FreeBSD
> with some such constraint?  How can I get more data?
> 
> The only way I know to ask Apache about its threads configuration
> is the Apache2::MPM->query facility.  Using this facility for all of
> the values noted in the Apache2::Const documentation yields:
> 
> MPMQ_MAX_DAEMON_USED(1) = -1
> MPMQ_IS_THREADED(2) = 1
> MPMQ_IS_FORKED(3) = 2
> MPMQ_HARD_LIMIT_DAEMONS(4) = 16
> MPMQ_HARD_LIMIT_THREADS(5) = 64
> MPMQ_MAX_THREADS(6) = 25
> MPMQ_MIN_SPARE_DAEMONS(7) = 0
> MPMQ_MIN_SPARE_THREADS(8) = 25
> MPMQ_MAX_SPARE_DAEMONS(9) = 0
> MPMQ_MAX_SPARE_THREADS(10) = 150
> MPMQ_MAX_REQUESTS_DAEMON(11) = 0
> MPMQ_MAX_DAEMONS(12) = 10
> 
> MPMQ_MAX_THREADS has the same value as ThreadsPerChild, but
> its name suggests that this number is a maximum.  Does this imply
> that this number may not be created as a child process starts?
> 
> Help will be much appreciated,
> cmac
> www.animalhead.com
> 
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