Messages in this thread | | | Date | Thu, 10 Jul 2008 09:50:47 +0200 | From | Wolfgang Grandegger <> | Subject | Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue? |
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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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