Messages in this thread | | | Date | Wed, 29 May 2013 13:06:20 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/x86: construct all sibling maps if smt |
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On Wed, May 29, 2013 at 12:26:01PM +0200, Andrew Jones wrote: > On Mon, May 27, 2013 at 07:09:00PM +0200, Andrew Jones wrote: > > Commit 316ad248307fb ("sched/x86: Rewrite set_cpu_sibling_map()") broke > > the construction of sibling maps, which also broke the booted_cores > > accounting. > > > > Before the rewrite, if smt was present, then each map was updated for > > each smt sibling. After the rewrite only cpu_sibling_mask gets updated, > > as the llc and core maps depend on 'has_mc = x86_max_cores > 1' instead. > > This leads to problems with topologies like the following > > > > (qemu -smp sockets=2,cores=1,threads=2) > > > > processor : 0 > > physical id : 0 > > siblings : 1 <= should be 2 > > core id : 0 > > cpu cores : 1 > > > > processor : 1 > > physical id : 0 > > siblings : 1 <= should be 2 > > core id : 0 > > cpu cores : 0 <= should be 1 > > > > processor : 2 > > physical id : 1 > > siblings : 1 <= should be 2 > > core id : 0 > > cpu cores : 1 > > > > processor : 3 > > physical id : 1 > > siblings : 1 <= should be 2 > > core id : 0 > > cpu cores : 0 <= should be 1 > > > > This patch restores the former construction by defining has_mc as > > (has_smt || x86_max_cores > 1). This should be fine as there were no > > (has_smt && !has_mc) conditions in the context. > > > > Signed-off-by: Andrew Jones <drjones@redhat.com> > > --- > > arch/x86/kernel/smpboot.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > > index 9c73b51817e47..886a3234eaff3 100644 > > --- a/arch/x86/kernel/smpboot.c > > +++ b/arch/x86/kernel/smpboot.c > > @@ -372,15 +372,15 @@ static bool __cpuinit match_mc(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o) > > > > void __cpuinit set_cpu_sibling_map(int cpu) > > { > > - bool has_mc = boot_cpu_data.x86_max_cores > 1; > > bool has_smt = smp_num_siblings > 1; > > + bool has_mc = has_smt || boot_cpu_data.x86_max_cores > 1; > > struct cpuinfo_x86 *c = &cpu_data(cpu); > > struct cpuinfo_x86 *o; > > int i; > > > > cpumask_set_cpu(cpu, cpu_sibling_setup_mask); > > > > - if (!has_smt && !has_mc) { > > + if (!has_mc) { > > cpumask_set_cpu(cpu, cpu_sibling_mask(cpu)); > > cpumask_set_cpu(cpu, cpu_llc_shared_mask(cpu)); > > cpumask_set_cpu(cpu, cpu_core_mask(cpu)); > > -- > > 1.8.1.4 > > > > Any acks? This patch fixes a regression. Also, in case anybody is > wondering, this is not the same regression as was already fixed with > > ceb1cbac8eda6 sched/x86: Calculate booted cores after construction of sibling_mask > > (Hmm, I probably should have renamed has_mc to has_mp, as the redefinition > expands its scope. I'm not sure if that deserves a v2 though.)
Right, took me a while to bend my brain around that code again -- I obviously don't have the best track record since this is the second bug in it since I rewrote the thing (with the intent of making it 'easier' to read ha!).
Yes, I think your patch is correct, and your suggestion of doing s/has_mc/has_mp/ seems a sensible one too.
Thanks!
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