cvs commit: src/sys/amd64/amd64 local_apic.c
src/sys/i386/acpica madt.c src/sys/i386/i386 local_apic.c
src/sys/kern subr_smp.c src/sys/sun4v/mdesc mdesc_init.c
jhb at freebsd.org
Mon Sep 24 09:13:24 PDT 2007
On Friday 21 September 2007 04:38:47 pm Attilio Rao wrote:
> 2007/9/21, John Baldwin <jhb at freebsd.org>:
> > On Tuesday 11 September 2007 06:54:09 pm Attilio Rao wrote:
> > > attilio 2007-09-11 22:54:09 UTC
> > >
> > > FreeBSD src repository
> > >
> > > Modified files:
> > > sys/amd64/amd64 local_apic.c
> > > sys/i386/acpica madt.c
> > > sys/i386/i386 local_apic.c
> > > sys/kern subr_smp.c
> > > sys/sun4v/mdesc mdesc_init.c
> > > Log:
> > > This is a follow-up, cleaning-up commit about recent changes involving
> > > topology foo functions.
> > > Working at the patch for topology problems in ia32/amd64 evicted some
> > > problems regarding functions ordering in the SI_SUB_CPU family of
> > > SYSINIT'ed subsystems.
> > > In order to avoid problems with new modified to involved functions, a
> > > correct ordering is not semantically specified for SI_SUB_CPU
> > > (for a larger view of the issue please visit:
> > >
> > Could you clarify exactly what ordering this does? AFAICT, nothing in
> > cpu_startup() requires the APIC to be up and running. If there were a
> > dependency, then that would be something for the MD architecture code to
> > IIUC, the problem was that you had 3 sysinit functions like this:
> > A - SI_ORDER_FIRST, cpu_startup()
> > B - SI_ORDER_FIRST, apic_init()
> > C - SI_ORDER_SECOND, mp_start()
> > Now mp_start() requires both A and B to have run on x86. What Peter did
> > originally was to move B to SI_ORDER_SECOND because he found that B needed
> > to run. That broke because C could end up running before B. However, the
> > actual patch that went into CVS left A and B as is and instead made them
> > independent of each other so B no longer depends on A. So, I don't think
> > you've solved an actual problem.
> I know exactly what was the problem as I diagnosed the problem when B
> was in SI_ORDER_FIRST and I diagnosed the problem when B was moved
> temporally in SI_ORDER_SECOND while C was taking this slot.
> Basically what about people adding code in A which introduces
> dependency with B? It results in a problem
> This ordering doesn't break anything and it makes the code safe for
> further changes.
It's a gratuitous change if you aren't actually _fixing_ anything. I think
there is a fundamental thing you are missing here though: it is ok to have
multiple SYSINIT's with the same subsystem and order if they are independent.
All device drivers register themselves with new-bus at the same subsystem and
order for example. There is no need to "dream up" a false ordering if it is
not needed. Now you have made B always come after A. What if a future code
change makes A depend on B? It is best to solve these problems when they
> > The madt.c change in this commit is plain wrong however and should be
> > reverted. If it was correct it would have needed to be done in amd64's
> > madt.c as well.
> Plain wrong?
> You mean maybe that it doesn't matter that (SI_ORDER_CPU -1) was
> shared with mptable_register()? And what about if someone adds
> dependency between the two? madt changes are perfectly working as they
> don't explicitly require to run before of mptable_register().
> And to be precise, there is no madt_register() in amd64, so I have no
> idea what are you speaking about. :(.
I guess you don't understand what these register routines do. The APIC code
basically is a driver framework and APIC drivers (well, I call them APIC
enumerators) register themselves with the core APIC code. These
drivers/enumerators are then probed and the highest priority wins. Having
these register routines at the same SYSINIT is identical to having all
new-bus drivers register themselves with new-bus at the same level. They
will never have any dependency on each other.
% grep madt_register amd64/acpica/madt.c
static void madt_register(void *dummy);
madt_register(void *dummy __unused)
SYSINIT(madt_register, SI_SUB_TUNABLES - 1, SI_ORDER_FIRST,
AMD64 looks for CPUs at at different time, so it uses SI_SUB_TUNABLES rather
than SI_SUB_CPU, but it still has both mptable_register() and madt_register()
at the same level/order and for a good reason.
> > The sun4v change is bogus as well as mdesc_init() doesn't depend on
> > cpu_startup() on sun4v at all, and it doesn't matter what order they run
> Reading this I think I see there is basically a misunderstanding of
> what I wanted to do: I don't want to fix an actual problem but the
> idea is to give to any function in SI_SUB_CPU a precise order in order
> to avoid mistakes as the last ones people get trying to fix topology.
> I think this is a legitimate idea.
> And in particular, I don't like the approach 'just do things when you
> need them'.
See above. Are you going to go throw and assign a static order to ever device
driver now just in case the one's registration routine might someday depend
> > Basically, I think at the least you should revert all the MD changes, and
> > change to subr_smp.c is basically a NOP.
> I'm not going to do this as the patch gives a precise ordering to all
> functions involved in SI_SUB_CPU, doesn't break anything.
> If you don't like the ordering due please just explain why.
It hardcodes an ordering that isn't there and that might have to be reworked
in the future if a real dependency does show up that is not the order you
currently just randomly chose.
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