On 2012-04-02 17:39, Gilles Chanteperdrix wrote: > On 02/24/2012 03:40 PM, Philippe Gerum wrote: >> On 02/24/2012 01:28 PM, Gilles Chanteperdrix wrote: >>> On 02/20/2012 05:46 PM, Philippe Gerum wrote: >>>> On 02/19/2012 08:43 PM, Gilles Chanteperdrix wrote: >>>>> >>>>> Hi, >>>>> >>>>> restarting the ipipe-core is the good opportunity to look a bit at our >>>>> current state and think about what we could improve. On ARM, at least, >>>>> the thing we could improve is the timer subsystem. A long time ago, >>>>> linux has switched to a system allowing to select at run-time which >>>>> timer to use, and we do not really benefit from this, what timer we use >>>>> is selected at compile time, resulting in a massive ifdefery on arm, and >>>>> even on x86, we have to select at compile time whether using the 8254 or >>>>> APIC, whereas we could decide to use whatever linux is using, even say >>>>> HPET, without any compilation option. That is assuming we want to move >>>>> the x86 timer-specific code from xenomai to I-pipe. >>>>> >>>>> The idea to reach this goal would be to add some ipipe specific members >>>>> to the struct clock_event_device, the way we do for the interrupt >>>>> controller: >>>>> - a CLOCK_EVT_FEAT_IPIPE would signal that the clockevent device is >>>>> ipipe capable, meaning that it implements the following callback >>>>> - ipipe_steal would be called when stealing the timer, we could decide >>>>> to call this callback either as part of ipipe_request_timer, or with a >>>>> specific ipipe_steal_timer call, currently we simply set >>>>> __ipipe_mach_timerstolen to 1, but it is pure luck that we never needed >>>>> something more complicated, besides, we may want to start a timer that >>>>> was not started by linux so, we would put its initialization here; >>>>> - ipipe_stolen would record whether the timer is stolen >>>>> - ipipe_min_delta_ticks, ipipe_max_delta_ticks would be used by the >>>>> ipipe_set_next_event callback >>>>> - ipipe_ack would be called to ack the timer interrupt the way we >>>>> currently do it currently on arm with __ipipe_mach_acktimer >>>>> - ipipe_set_next_event would program the next timer shot, the way it is >>>>> currently done in __ipipe_mach_set_dec. >>>>> >>>>> All this is pretty straightforward, but there is still a question: how >>>>> does ipipe_request_timer select a timer. The idea is that on platform >>>>> without PIC muting, it is probably more efficient to use the same timer >>>>> for linux and xenomai. But on platforms with PIC muting, we could want >>>>> to select a different timer for linux and xenomai, but how do we find >>>>> it, what if linux has not selected a timer because it is unusable on >>>>> that platform? >>>> >>>> Checking the clock device mode for CLOCK_EVT_MODE_SHUTDOWN, and falling >>>> back to sharing the active kernel tick device + disabling PIC muting? >>> >>> OK. Another question is: do we want to move x86 timer handling from >>> xenomai to ipipe. If not, we have to find a way to support the two >>> possible configurations. What we could do is using the timer name in >>> ipipe_request_tickdev: if a timer name is supplied, we keep the old >>> implementation, if no timer name is supplied, we use the newho >>> implementation which looks for the best candidate with the >>> CLOCK_EVT_FEAT_IPIPE bit. >>> >>> >> >> Yes, makes sense. At any rate, handling the real-time timer the way we >> want for Xenomai directly from the pipeline is the only sane option. We >> only have to be careful about backward compatibility of the newest core >> pipelines with 2.6.x, until we stop maintaining this branch in favor of >> 3.x. We may also move ipipe_request_tckdev() to the compat module fully, >> removing it from the current API if that makes sense. >> > > For those who would like to follow, the result, a bit different from what > was originally planned is the interface implemented by this file: > http://git.xenomai.org/?p=ipipe-gch.git;a=blob;f=kernel/ipipe/timer.c;h=b9936469652d8fe998157d155fda77df81f0425a;hb=52d36aa86d5c5d463d86d384ad717f26ec96ef8c > > And ARM and x86 architectures were re-factored over this interface. As > an example, the implementation of x86 timers is in this patch: > http://git.xenomai.org/?p=ipipe-gch.git;a=commitdiff;h=52d36aa86d5c5d463d86d384ad717f26ec96ef8c;hp=675a8ed4365eb1f23b098f913caf40e4dc792b80 > > 8254, local APIC and HPET in legacy mode were tested, even selected > at run-time. Only per-cpu HPET remains to be tested (the hardware > I have does not support it).
FWI, QEMU (w/ or w/o KVM) can emulated enough HPET timers, also with MSI support, but that was broken in I-pipe last time I checked. Use -global hpet.timers=4 (or more for more CPUs) and -global hpet.msi=on. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux _______________________________________________ Adeos-main mailing list Adeos-main@gna.org https://mail.gna.org/listinfo/adeos-main
