Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue?

[Wolfgang Grandegger <wg@grandegger.com>]

Hi Fu (without n)

Luotao Fu wrote:
> Hi Wolfgang,
> 
> Wolfgang Grandegger wrote:
>> Hi Fun,
> 
> What's so funny? ;-)

Ah, oh, just a funny typo ;-).

> [...]
> 
>> But as Steven pointed out, the preempt_enable_noresched at that place
>>  might be illegal, anyway. In 2.6.25-rt, trace_mark() is no longer
>> used and I do not see an improvement with CONFIG_RCU_TRAC any more.
>> Latencies go up to 600us. I also tried with CONFIG_RCU_BOOST
>> disabled, but it did not improve the latencies. Actually, I still
>> measure significantly different latencies with 2.6.24.4-rt4,
>> 2.6.24.7-rt14 and 2.6.25.8-rt7, which is quite frustrating. As you
>> seem not be able to reproduce my high latencies, I wonder if there
>> are some toolchain or glibc related issues.
> 
> I took a quick look into the rcppreempt boost stuff in 2.6.24-rt and
> 2.6.25-rt. As you have mentioned, trace_mark is no more used in
> 2.6.24-rt. Instead of that flags are used to detect if the task is
> preempted. It might indeed probably be some toolchain issue.
> My powerpc toolchain I'm using here contains gcc 4.1.2 and glibc 2.5

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?

Wolfgang.