Re: [Xenomai-core] Potential problem with rt_eepro100

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
>>> Anyway, after some thoughts, I think we are going to try and make the
>>> current situation work instead of going back to the old way.
>>>
>>> You can find the patch which attempts to do so here:
>>> http://sisyphus.hd.free.fr/~gilles/sched_status.txt
>> Ack. At last, this addresses the real issues without asking for
>> regression funkiness: fix the lack of barrier before testing XNSCHED in
> 
> Check the kernel, we actually need it on both sides. Wherever the final
> barriers will be, we should leave a comment behind why they are there.
> Could be picked up from kernel/smp.c.

We have it on both sides: the non-local flags are modified while holding
the nklock. Unlocking the nklock implies a barrier.

> 
>> the xnpod_schedule pre-test, and stop sched->status trashing due to
>> XNINIRQ/XNHTICK/XNRPICK ops done un-synced on nklock.
>>
>> In short, this patch looks like moving the local-only flags where they
>> belong, i.e. anywhere you want but *outside* of the status with remotely
>> accessed bits. XNRPICK seems to be handled differently, but it makes
>> sense to group it with other RPI data as you did, so fine with me.
> 
> I just hope we finally converge over a solution. Looks like all
> possibilities have been explored now. A few more comments on this one:
> 
> It probably makes sense to group the status bits accordingly (both their
> values and definitions) and briefly document on which status field they
> are supposed to be applied.

Ok, but I wanted them to not use the same values, so that we can use the
sched->status | sched->lstatus trick in xnpod_schedule. Something is
lacking too: we probably need to use sched->status | sched->lstatus for
display in /proc.

> 
> I do not understand the split logic - or some bits are simply not yet
> migrated. XNHDEFER, XNSWLOCK, XNKCOUT are all local-only as well, no?
> Then better put them in the _local_ status field, that's more consistent
> (and would help if we once wanted to optimize their cache line usage).

Maybe the naming is not good the. ->status is everything which is
modified under nklock, ->lstatus is for XNINIRQ and XNHTICK which are
modified without holding the nklock.

> 
> The naming is unfortunate: status vs. lstatus. This is asking for
> confusion and typos. They must be better distinguishable, e.g.
> local_status. Or we need accessors that have debug checks built in,
> catching wrong bits for their target fields.

I agree.

> 
> Good catch of the RPI breakage, Gilles!

-- 
                                                                Gilles.