On Thu, Oct 21, 2021 at 9:43 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Wed, Oct 20, 2021 at 10:36:19PM +0200, Peter Zijlstra wrote: > > > OK, I think I see what's happening. > > > > AFAICT cacheinfo.c does *NOT* set l2c_id on AMD/Hygon hardware, this > > means it's set to BAD_APICID. > > > > This then results in match_l2c() to never match. And as a direct > > consequence set_cpu_sibling_map() will generate cpu_l2c_shared_mask with > > just the one CPU set. > > > > And we have the above result and things come unstuck if we assume: > > SMT <= L2 <= LLC > > > > Now, the big question, how to fix this... Does AMD have means of > > actually setting l2c_id or should we fall back to using match_smt() for > > l2c_id == BAD_APICID ? > > The latter looks something like the below and ought to make EPYC at > least function as it did before. > > > --- > arch/x86/kernel/smpboot.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 849159797101..c2671b2333d1 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -472,7 +472,7 @@ static bool match_l2c(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o) > > /* Do not match if we do not have a valid APICID for cpu: */ > if (per_cpu(cpu_l2c_id, cpu1) == BAD_APICID) > - return false; > + return match_smt(c, o); /* assume at least SMT shares L2 */ Rather than making a fake cluster_cpus and cluster_cpus_list which will expose to userspace through /sys/devices/cpus/cpux/topology, could we just fix the sched_domain mask by the below? It will be odd to users that a cpu has BAD cluster_id but has "meaningful" cluster_cpus and cluster_cpus_list in sys. diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 5094ab0bae58..0f9d706a7507 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -687,6 +687,15 @@ const struct cpumask *cpu_coregroup_mask(int cpu) const struct cpumask *cpu_clustergroup_mask(int cpu) { + /* + * if L2(cluster) is not represented, make cluster sched_domain + * same with smt domain, so that this redundant sched_domain can + * be dropped and we can avoid the complaint "the SMT domain not + * a subset of the cluster domain" + */ + if (cpumask_subset(cpu_l2c_shared_mask(cpu), cpu_smt_mask(cpu))) + return cpu_smt_mask(cpu); + return cpu_l2c_shared_mask(cpu); } > > /* Do not match if L2 cache id does not match: */ > if (per_cpu(cpu_l2c_id, cpu1) != per_cpu(cpu_l2c_id, cpu2)) Thanks Barry
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