Le Mon, 25 Jul 2016 16:01:31 +1000, David Gibson <da...@gibson.dropbear.id.au> a écrit :
> On Fri, Jul 22, 2016 at 01:10:36PM +0200, Greg Kurz wrote: > > The goal of this patch is to have a stable core-id which does not depend > > on any DT related semantics, which involve non-obvious computations on > > modern PowerPC server cpus. > > > > With this patch, the DT core id is computed on-demand as: > > > > (core-id / smp_threads) * smt > > > > where smt is the number of threads per core in the host. > > > > This formula should be consolidated in a helper since it is needed in > > several places. > > It's a little odd you node this but don't do so. > I was too busy packing for holidays already :) and I think the consolidation work can be addressed in followup patches. Cheers from Brittany, under the rain. -- Greg > > Other uses for core-id includes: compute a stable cpu_index (which > > allows random order hotplug/unplug without breaking migration) and > > NUMA. > > > > Signed-off-by: Greg Kurz <gr...@kaod.org> > > --- > > > > It was first suggested here: > > > > https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg01727.html > > > > and as option 1) in the following discussion on IRC: > > > > <dwg> imammedo, basically the options are: 1) change core-ids to be > > 0, 1, .. n and compute cpu_index as core_id * threads + thread#, or > > 2) leave core-ids as they are and calculate cpu_index as > > core-id / smt * threads + thread# > > > > It is based on David's ppc-for-2.7 branch (commit bb6268f35f457). > > > > It is lightly tested but I could at least do in-order > > hotplug/unplug. > > I think this is basically the right approach, and I've applied to > ppc-for-2.7. Here's my plan for what to do about all this id stuff: > > 1. Merge this to ppc-for-2.7 (done) > 2. Assuming there are now show-stoppers in testing, send a pull > request tomorrow > 3. Once this is merged, try to get Igor's series (or a respin of it) > in ASAP. > > I'm hoping that will give us good-enough hotplug for 2.7. > > In the 2.8 timeframe, I want to: > 4. Disconnect KVM vcpu ID from dt_id, instead calculate it from (now > stable) cpu_index > 5. Remove dt_id as a cpu field - instead just compute DT ids from > the (now stable) cpu_index when we build the DT > 6. (for new machine type versions) Change DT ID assignment, so it > no longer depends on kvmppc_smt_threads(). The current scheme > means that migration between hosts with different native SMT > values won't work, which is unfortunate. I suspect there may be > other problems with any real situation where that's the case, > but nontheless it's a silly restriction. > > Nice to have but bigger scope things for 2.8: > 7. Update archs to they *all* call cpu_exec_init() / cpu_exec_exit() > at realize / unrealize time instead of init / finalize time. > 8. Update all archs and machines to use stable cpu_index >
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