Luotao Fu wrote:
Hi Wolfgang,
On Wed, Jul 09, 2008 at 03:15:01PM +0200, Wolfgang Grandegger wrote:
Hi Fu (without n)
....
OK, in the past you have been able to reproduce the high latencies with
2.6.24-rt1 and CONFIG_RCU_TRACE disabled, IIRC. Did you use a different
toolchain at that time?
Nope. As mentioned above, trace_mark() does some "real" works (what ever it is.),
while the new mechahnismen use flags to remember the state of preemption. Maybe
I don't known what you refer to, but in __rcu_preempt_unboost() of 2.6.25.8-rt7,
the trace code simply increments a counter:
static void rcu_trace_boost_##type(struct rcu_boost_dat *rbd) \
{ \
rbd->rbs_stat_##type++; \
}
and that's the reason why latency is not affected by switching CONFIG_RCU_TRACE
on (while trace_mark uses preempt_disable/preempt_enable around).
something here got optimized away? I take for grant, that you use gcc in your
toolchain. Which version do you have?
The ELDK v4.2 uses:
ppc_6xx-gcc (GCC) 4.2.2
and
GLIBC v2.6
But I measured the same latencies with ELDK v4.1:
ppc_6xx-gcc (GCC) 4.0.0 (DENX ELDK 4.1 4.0.0)
GLIBC v2.3.5
Wolfgang.
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