Re: [Xenomai-help] (WARNING!!! PGP with incorrect signature) Re: Time

[Dirk Eibach <eibach@domain.hid>]

jan.kiszka@domain.hid wrote:
> Dirk Eibach wrote:
>> gilles.chanteperdrix@xenomai.org wrote:
>>> On 8/17/07, Dirk Eibach <eibach@domain.hid> wrote:
>>>> gilles.chanteperdrix@xenomai.org wrote:
>>>>> Dirk Eibach wrote:
>>>>>  > Hello,
>>>>>  >
>>>>>  > I'm wondering how long a rt_mutex_acquire is supposed to take on a PPC405
>>>>>  > platform. I'm getting times about 50 usec here, which is too much for my
>>>>>  > application. Is anything wrong in my kernel/xenomai configuration or is
>>>>>  > this time to expected?
>>>>>
>>>>> How do you measure this ? Are you sure the mutex is free when you try to
>>>>> acquire it ?
>>>>>
>>>> I prepared a small testcase. It shows about 8.300 ticks, which is about 30
>>>> usec on my platform (266MHz).
>>> Did you try to call ppc_getcounter twice in a raw to measure the
>>> overhead of this function ?
>> Calling ppc_getcounter twice in a raw results in 116 ticks.
> 
> Is that service RT-safe, means does it stay in user space and issue no
> Linux syscall? Maybe some of the PPC gurus can comment on this as well
> (/me is lacking comparative numbers).

This service should be RT-safe as it consists only of a few assembly 
commands that read the timestamp counter (which is allowed from userspace).

> 
> Besides this, you may want to try running the latency tracer on your
> scenario. xntrace_user_start() and xntrace_user_stop(0) would frame the
> path you want to measure, /proc/ipipe/trace/frozen will show its kernel
> side. For sure, that tool will increase the latency even more, but it
> may show better what goes on.

Here we go (start, acquire, stop):

I-pipe frozen back-tracing service on 2.6.18/ipipe-1.5-00
------------------------------------------------------------
Freeze: 2785703857177 cycles, Trace Points: 30 (+10)

  +--------------- Hard IRQs ('|': locked)
  |             +- Delay flag ('+': > 1 us, '!': > 10 us)
  |             |
   Type     Time   Function (Parent)
: func      -49+  xnshadow_sys_trace (hisyscall_event)
: func      -46   ipipe_trace_frozen_reset (xnshadow_sys_trace)
: func      -45+  __ipipe_global_path_lock (ipipe_trace_frozen_reset)
:|begin     -44+  __ipipe_global_path_lock (ipipe_trace_frozen_reset)
:|end       -41+  __ipipe_global_path_unlock (ipipe_trace_frozen_reset)
:|begin     -39+  __ipipe_dispatch_event (__ipipe_syscall_root)
:|end       -38+  __ipipe_dispatch_event (__ipipe_syscall_root)
: func      -34+  __ipipe_syscall_root (DoSyscall)
: func      -33+  __ipipe_dispatch_event (__ipipe_syscall_root)
:|begin     -31+  __ipipe_dispatch_event (__ipipe_syscall_root)
:|end       -30+  __ipipe_dispatch_event (__ipipe_syscall_root)
: func      -29+  hisyscall_event (__ipipe_dispatch_event)
: func      -27+  __rt_mutex_acquire (hisyscall_event)
: func      -25+  xnregistry_fetch (__rt_mutex_acquire)
:|begin     -24+  xnregistry_fetch (__rt_mutex_acquire)
:|func      -22+  __ipipe_restore_pipeline_head (xnregistry_fetch)
:|end       -20+  __ipipe_restore_pipeline_head (xnregistry_fetch)
: func      -19+  rt_mutex_acquire (__rt_mutex_acquire)
:|begin     -17+  rt_mutex_acquire (__rt_mutex_acquire)
:|func      -15+  __ipipe_restore_pipeline_head (rt_mutex_acquire)
:|end       -14+  __ipipe_restore_pipeline_head (rt_mutex_acquire)
:|begin     -12+  __ipipe_dispatch_event (__ipipe_syscall_root)
:|end       -11+  __ipipe_dispatch_event (__ipipe_syscall_root)
: func       -8+  __ipipe_syscall_root (DoSyscall)
: func       -6+  __ipipe_dispatch_event (__ipipe_syscall_root)
:|begin      -5+  __ipipe_dispatch_event (__ipipe_syscall_root)
:|end        -4+  __ipipe_dispatch_event (__ipipe_syscall_root)
: func       -2+  hisyscall_event (__ipipe_dispatch_event)
: func       -1+  xnshadow_sys_trace (hisyscall_event)
< freeze      0   xnshadow_sys_trace (hisyscall_event)
  |begin       1   __ipipe_dispatch_event (__ipipe_syscall_root)
  |end         3   __ipipe_dispatch_event (__ipipe_syscall_root)
   func       55   __ipipe_syscall_root (DoSyscall)
   func       57   __ipipe_dispatch_event (__ipipe_syscall_root)
  |begin      58   __ipipe_dispatch_event (__ipipe_syscall_root)
  |end        60   __ipipe_dispatch_event (__ipipe_syscall_root)
   func       61   hisyscall_event (__ipipe_dispatch_event)
   func       63   xnshadow_relax (hisyscall_event)
  |begin      64   xnshadow_relax (hisyscall_event)
  |func       66   schedule_linux_call (xnshadow_relax)

Cheers
-- 
Dirk Eibach
Entwicklung
Guntermann & Drunck GmbH Systementwicklung