Re: [Xenomai-core] [PATCH] nucleus: Fix interrupt handler tails
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
Re: [Xenomai-core] [PATCH] nucleus: Fix interrupt handler tails
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. -- Gilles. ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
Re: [Xenomai-core] [PATCH] nucleus: Fix interrupt handler tails
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. 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
Re: [Xenomai-core] [PATCH] nucleus: Fix interrupt handler tails
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 ? -- Gilles. ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
Re: [Xenomai-core] [PATCH] nucleus: Fix interrupt handler tails
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. 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
Re: [Xenomai-core] [PATCH] nucleus: Fix interrupt handler tails
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. -- Gilles. ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
