osmo-bts / osmo-pcu profiling results

[Harald Welte]

Hi all,

I've been doing some profiling on osmo-bts recently (on sysmobts
hardware, which has only a relatively slow ARM926 CPU core), and the two
things that show up most are:

* msgb_alloc() -> talloc_zero() -> malloc
  this can be alleviated somewhat by using talloc pools.  For some
  reason the pools don't remove all of the malloc() calls.

* vfprintf() and friends, from logp() statements.  The sad part is that
  calls like gsm_lchan_name() are of course executed beefore the call
  into logp(), at which point the vfprintf/sprintf/... for arguments has
  already been executed, and only the last/final one hasn't happened
  yet.

  Here we can do two things: Calls like gsm_lchan_name() don't need to
  happen all the time, as the lchan name is static and can be generated
  once at the time gsm_lchan is created.  I implemented that in osmo-bts
  (and openbsc, as it's from gsm_data_shared).

  The second idea would be to expand the LOGP() macro a bit in a way to
  ensure the the checking whether the log line is enabled _before_ the
  arguments (and thus associated function calls) are evaluated.  Any
  ideas on that?

After a brief look at osmo-pcu profiling, it looks like in the
attached picture.  We cannot do much about the __copy_to_user_std,
do_select and core_sys_select, as those are kernel side.

However, there again we see vfprintf and friends, mostly via
gprs_rlcmac_tbf::name() - and of course the msgb_alloc() and msgb_free()
going through talloc and finally malloc.

So the same strategies as above could (and probably should) be applied
to osmo-pcu.

Regards,
	Harald
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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