[Xenomai] "RT throttling" issue

Jochen Behnke JK.Behnke at web.de
Tue Dec 8 13:12:00 CET 2015


> Gesendet: Dienstag, 08. Dezember 2015 um 12:05 Uhr
> Von: "Gilles Chanteperdrix" <gilles.chanteperdrix at xenomai.org>
> An: "Jochen Behnke" <JK.Behnke at web.de>
> Cc: xenomai at xenomai.org
> Betreff: Re: [Xenomai] "RT throttling" issue
> On Tue, Dec 08, 2015 at 11:42:32AM +0100, Jochen Behnke wrote:
> > "ipipe_root_only" also occasionally has long delay times.
> > Is ipipe_root_only run when Linux is executing?
> > Is this critical?
> > See extract below.
> > ================== start: extract from frozen file
> > ================================
> > : +func -420045+ 1.443 ipipe_root_only+0x4
> > (copy_to_user+0x31)
> > : +func -420044 0.260 __ipipe_syscall_root+0x5
> > (sysenter_past_esp+0x5b)
> > : +func -420043 0.200 sys_time+0x5
> > (sysenter_do_call+0x12)
> > : +func -420043 0.210 get_seconds+0x3
> > (sys_time+0xf)
> > : +func -420043! 3910.393 ipipe_root_only+0x4
> > (sys_time+0x1c)
> > :| +func -416132 0.651 __ipipe_handle_irq+0x5
> > (common_interrupt+0x2c)
>
> Hi,
>
> What you have here is a system call to the "time" function from a
> task scheduled by Linux scheduler. When the system call is finished,
> the system returns to user-space. ipipe_root_only happens to be the
> last function called before the return to user-space and before the
> next interrupt. ipipe_root_only gets then charged for the time spent
> in user-space.
>
> What version of the I-pipe patch are you using on which
> architecture? On some architectures we try to create trace points
> when entering and leaving the kernel to avoid this issue (with the
> added benefit that the user-space value of the PC gets printed, this
> may be useful if you have an infinite loop).
Xenomai:      2.6.4 githead
Architecture: x86
Platform:     Atom E640/E660
I-pipe patch: ipipe-core-3.8.13-x86-4.patch


Regards
Jochen
 
 



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