On 2011-06-17 13:26, Gilles Chanteperdrix wrote: > On 06/17/2011 01:22 PM, Jan Kiszka wrote: >> On 2011-06-17 13:06, Gilles Chanteperdrix wrote: >>> On 06/17/2011 01:03 PM, Jan Kiszka wrote: >>>> On 2011-06-17 12:55, Gilles Chanteperdrix wrote: >>>>> On 06/17/2011 11:26 AM, Jan Kiszka wrote: >>>>>> Our current interrupt handlers assume that they leave over the same task >>>>>> and CPU they entered. But CONFIG_XENO_HW_UNLOCKED_SWITCH and commit >>>>>> f6af9b831c broke this assumption: xnpod_schedule invoked from the >>>>>> handler tail can now actually trigger a domain migration >>>>> >>>>> What unlocked context swith introduce from my point of view is simply >>>>> sections where interrupt happen which do not reschedule. >>>>> >>>>> f6af9b831c introduce a rescheduling point, but does not change what >>>>> happens during the interrupt handler either. >>>>> >>>>> So, I do not really understand this commit message. Either we can assume >>>>> that interrupt handlers migrate tasks or not, but this does not seem to >>>>> have anything to do with unlocked context switches or commit f6af9b831c. >>>> >>>> It has: Task is about to relax, re-enables interrupts in >>>> xnpod_resume_thread, IRQ hits, handler is entered over the relaxing RT >>>> task, xnpod_schedule in its tail performs the switch to root, which then >>>> continues to relaxed task, IRQ tail resumes over a different task, on >>>> SMP potentially also on a different CPU. I can send you a the trace if >>>> you want to have a closer look. >>> >>> Ok. Got it. But what has this to do with unlocked context switches ? >> >> Also before commit f6af9b831c, there was a window with enabled IRQs in >> the relaxation path. So the above scenario should have been possible >> even earlier. > > Unlocked context swith enables irqs, but sets the XNSWLOCK bit, so, no > other rescheduling can take place.
Ah, OK. Will remove that from the commit log. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
