AW: AW: [PATCH v3 3/3] i386: Port to RTEMS

[Jan.Sommer at dlr.de]

Von: Sebastian Huber [mailto:sebastian.huber at embedded-brains.de] 
Gesendet: Montag, 23. März 2020 14:20
An: Sommer, Jan; devel at rtems.org
Betreff: Re: AW: [PATCH v3 3/3] i386: Port to RTEMS
> 
> 
> > -----Ursprüngliche Nachricht-----
> > Von: devel [mailto:devel-bounces at rtems.org] Im Auftrag von
> > Jan.Sommer at dlr.de
> > Gesendet: Montag, 23. März 2020 13:50
> > An: sebastian.huber at embedded-brains.de; devel at rtems.org
> > Betreff: AW: [PATCH v3 3/3] i386: Port to RTEMS
> > 
> > 
> > 
> > > -----Ursprüngliche Nachricht-----
> > > Von: Sebastian Huber [mailto:sebastian.huber at embedded-brains.de]
> > > Gesendet: Montag, 23. März 2020 10:59
> > > An: Sommer, Jan; devel at rtems.org
> > > Betreff: Re: [PATCH v3 3/3] i386: Port to RTEMS
> > >
> > > On 23/03/2020 09:06, Jan Sommer wrote:
> > >
> > > > @@ -4597,7 +4599,12 @@ iflib_device_register(device_t dev, void *sc,
> > > if_shared_ctx_t sctx, if_ctx_t *ct
> > > >   	/* Set up cpu set.  If it fails, use the set of all CPUs. */
> > > >   	if (bus_get_cpus(dev, INTR_CPUS, sizeof(ctx->ifc_cpus), &ctx-
> > > >ifc_cpus) != 0) {
> > > >   		device_printf(dev, "Unable to fetch CPU list\n");
> > > > +#ifndef __rtems__
> > > >   		CPU_COPY(&all_cpus, &ctx->ifc_cpus);
> > > > +#else /* __rtems__ */
> > > > +		cpuset_t cpus = {all_cpus};
> > > > +		CPU_COPY(&cpus, &ctx->ifc_cpus);
> > > > +#endif /* __rtems__ */
> > > >   	}
> > > >   	MPASS(CPU_COUNT(&ctx->ifc_cpus) > 0);
> > >
> > > What is the reason for this change?
> > >
> > 
> > For RTEMS the all_cpus variable has been replaced in freebsd/sys/sys/smp.h
> > to " #define all_cpus 1U".
> > The additional variable is there because CPU_COPY requires an address.
> > 
> > > Could you please move the changes in non-x86 specific files to a
> > > separate commit. Especially the <sys/callout.h> is an important header
> > > file used across all architectures.
> > 
> Ok, problems like this are an indication that you try to use a feature which is 
> not really supported. I would first try to understand what the purpose of the
> ifc_cpus is. Maybe this stuff could be disabled completely.

Ok, I investigated the issue further. 
If I understand the RTEMS specific settings in sys/smp.h correctly, rtems-libbsd always assumes to run on a single core?

ifc_cpus is the map of active CPUs, i.e. for RTEMS it should be 1, and is used to determine the queue sizes.
It is only initialized once from all_cpus, but with CPU_COPY, which requires an address as source.
In FreeBSD all_cpus is a variable, for RTEMS it is only a define producing a compile error.

As far as I see it, we could either use a temporary variable as above or maybe an int for the all_cpus in sys/smp.h instead of the define.
However the latter would move the assignment to a c-file, thus making it harder to find. Do you have any other idea?