On Fri, Jul 08, 2016 at 12:59:59PM +0200, Igor Mammedov wrote: > On Fri, 8 Jul 2016 17:39:52 +1000 > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > On Fri, Jul 08, 2016 at 12:11:12PM +0530, Bharata B Rao wrote: > > > On Fri, Jul 08, 2016 at 03:24:13PM +1000, David Gibson wrote: > > > > On Thu, Jul 07, 2016 at 08:20:23PM +0530, Bharata B Rao wrote: > > > > > Conditonally set stable_cpu_id for CPU threads that are created as > > > > > part > > > > > of spapr CPU cores. The use of stable_cpu_id is enabled for > > > > > pseries-2.7 > > > > > onwards. > > > > > > > > > > Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com> > > > > > --- > > > > > hw/ppc/spapr_cpu_core.c | 7 +++++++ > > > > > 1 file changed, 7 insertions(+) > > > > > > > > > > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c > > > > > index b104778..0ec3513 100644 > > > > > --- a/hw/ppc/spapr_cpu_core.c > > > > > +++ b/hw/ppc/spapr_cpu_core.c > > > > > @@ -293,8 +293,15 @@ static void spapr_cpu_core_realize(DeviceState > > > > > *dev, Error **errp) > > > > > for (i = 0; i < cc->nr_threads; i++) { > > > > > char id[32]; > > > > > obj = sc->threads + i * size; > > > > > + CPUState *cs; > > > > > > > > > > object_initialize(obj, size, typename); > > > > > + cs = CPU(obj); > > > > > + > > > > > + /* Use core_id (which is actually cpu_dt_id) as stable CPU > > > > > id */ > > > > > + if (cs->has_stable_cpu_id) { > > > > > + cs->stable_cpu_id = cc->core_id + i; > > > > > + } > > > > > > > > Testing cs->has_stable_cpu_id here in machine type specific code seems > > > > really weird. It's the machine type that knows whether it has a > > > > stable ID to give to the CPU or not, rather than the other way around. > > > > > > > > Since we haven't yet had a release with cpu cores, I think the right > > > > thing is for cpu_core to unconditionally set the stable ID (and set > > > > has_stable_id to true). > > > > > > Right, we can set cpu_stable_id unconditionally here since this code path > > > (core realize) will be taken only for pseries-2.7 onwards. has_stable_id > > > will get set as part of the property we defined in SPAPR_COMPAT_2_7. > > > > Hrm, that's true. But when you describe it like that it sounds like a > > really non-obvious and fragile dependency between different components. > that's how compat stuff is typically done for devices, > CPUs shouldn't be an exception. > (consistency with other devices helps here in long run) > > > > > The backup path that does thread-based cpu > > > > init, can set has_stable_id to false (if that's not the default). > > > > > > Default is off, but turning it on for 2.7 will be inherited by 2.6 > > > and others below. Hence I have code to explicitly disable this prop > > > for 2.6 and below via SPAPR_COMPAT_2_6. > > > > This is all seeming terribly awkward. > Typically default is set the way so new machine type doesn't have > to enable it explicitly. > > However the way it's done here helps not to touch/check every user > that uses cpu_index, limiting series impact only to code that > asks for it, it look a lot safer to got this rout for now. > > > > Can we try investigating a > > different approach: > > > > 1. Rename cpu_index to cpu_id, but it's still used in the same > > places it's used. > > > > 2. Remove assumptions that cpu_id values are contiguous or > > dense > > > > 3. Machine type decides whether it wants to populate the cpu_id > > values explicitly, or leave it to generic code to calculate > > them as cpu_index is calculated now. > > > > 4. Ideally, generic code enforces that the machine type populates > > either all or none of the cpu_id values. > > > > Does that seem workable? > Ideally we will get there some day (and may be get rid of cpu_index > altogether), > but for now it seems too invasive with a lot of chances to introduce non > obvious > regression.
Yes, that's a risk. But I'm basically no longer convinced that it's any higher than the risk of the same thing with the current approach. > So I'd keep approach used in this series. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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