From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philippe Gerum In-Reply-To: <4A0BF054.3040308@domain.hid> References: <4A0AC1C8.4050006@domain.hid> <4A0AC3F9.9090103@domain.hid> <4A0AC8A6.1000701@domain.hid> <1242220962.26544.955.camel@domain.hid> <4A0AE726.5090107@domain.hid> <1242230121.26544.977.camel@domain.hid> <4A0AF109.5050804@domain.hid> <1242247840.26544.981.camel@domain.hid> <4A0BF054.3040308@domain.hid> Content-Type: text/plain Date: Thu, 14 May 2009 12:49:17 +0200 Message-Id: <1242298157.6816.10.camel@domain.hid> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] [PATCH] Fix host IRQ propagation List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: xenomai-core On Thu, 2009-05-14 at 12:20 +0200, Jan Kiszka wrote: > Philippe Gerum wrote: > > On Wed, 2009-05-13 at 18:10 +0200, Jan Kiszka wrote: > >> Philippe Gerum wrote: > >>> On Wed, 2009-05-13 at 17:28 +0200, Jan Kiszka wrote: > >>>> Philippe Gerum wrote: > >>>>> On Wed, 2009-05-13 at 15:18 +0200, Jan Kiszka wrote: > >>>>>> Gilles Chanteperdrix wrote: > >>>>>>> Jan Kiszka wrote: > >>>>>>>> Hi Gilles, > >>>>>>>> > >>>>>>>> I'm currently facing a nasty effect with switchtest over latest git head > >>>>>>>> (only tested this so far): running it inside my test VM (ie. with > >>>>>>>> frequent excessive latencies) I get a stalled Linux timer IRQ quite > >>>>>>>> quickly. System is otherwise still responsive, Xenomai timers are still > >>>>>>>> being delivered, other Linux IRQs too. switchtest complained about > >>>>>>>> > >>>>>>>> "Warning: Linux is compiled to use FPU in kernel-space." > >>>>>>>> > >>>>>>>> when it was started. Kernels are 2.6.28.9/ipipe-x86-2.2-07 and > >>>>>>>> 2.6.29.3/ipipe-x86-2.3-01 (LTTng patched in, but unused), both show the > >>>>>>>> same effect. > >>>>>>>> > >>>>>>>> Seen this before? > >>>>>>> The warning about Linux being compiled to use FPU in kernel-space means > >>>>>>> that you enabled soft RAID or compiled for K7, Geode, or any other > >>>>>> RAID is on (ordinary server config). > >>>>>> > >>>>>>> configuration using 3DNow for such simple operations as memcpy. It is > >>>>>>> harmless, it simply means that switchtest can not use fpu in kernel-space. > >>>>>>> > >>>>>>> The bug you have is probably the same as the one described here, which I > >>>>>>> am able to reproduce on my atom: > >>>>>>> https://mail.gna.org/public/xenomai-help/2009-04/msg00200.html > >>>>>>> > >>>>>>> Unfortunately, I for one am working on ARM issues and am not available > >>>>>>> to debug x86 issues. I think Philippe is busy too... > >>>>>> OK, looks like I got the same flu here. > >>>>>> > >>>>>> Philippe, did you find out any more details in the meantime? Then I'm > >>>>>> afraid I have to pick this up. > >>>>> No, I did not resume this task yet. Working from the powerpc side of the > >>>>> universe here. > >>>> Hoho, don't think this rain here over x86 would have never made it down > >>>> to ARM or PPC land! ;) > >>>> > >>>> Martin, could you check if this helps you, too? > >>>> > >>>> Jan > >>>> > >>>> (as usual, ready to be pulled from 'for-upstream') > >>>> > >>>> ---------> > >>>> > >>>> Host IRQs may not only be triggered from non-root domains. > >>> Are you sure of this? I can't find any spot where this assumption would > >>> be wrong. host_pend() is basically there to relay RT timer ticks and > >>> device IRQs, and this only happens on behalf of the pipeline head. At > >>> least, this is how rthal_irq_host_pend() should be used in any case. If > >>> you did find a spot where this interface is being called from the lower > >>> stage, then this is the root bug to fix. > >> I haven't studied the I-pipe trace /wrt this in details yet, but I could > >> imagine that some shadow task is interrupted in primary mode by the > >> timer IRQ and then leaves the handler in secondary mode due to whatever > >> events between schedule-out and in at the end of xnintr_clock_handler. > >> > > > > You need a thread context to move to secondary, I just can't see how > > such scenario would be possible. > > Here is the trace of events: > > => Shadow task starts migration to secondary > => in xnpod_suspend_thread, nklock is briefly released before > xnpod_schedule Which is the root bug. Blame on me; this recent change in -head breaks a basic rule a lot of code is based on: a self-suspending thread may not be preempted while scheduling out, i.e. suspension and rescheduling must be atomically performed. xnshadow_relax() counts on this too. > => timer IRQ intercepts > => as the current CPU is marked for reschedule, we enter xnpod_schedule > before propagating the host tick > => once the migrating thread comes in again, it will run the > xnintr_clock_handler tail, i.e. xnarch_relay_tick, already over the > root domain Ok, makes sense now. However, this can't happen with 2.4 which has no such lock release in xnpod_suspend_thread(). So the question is: was the "lost tick" bug observed also on 2.4, or not? > > Jan > -- Philippe.