[PATCH v3] x86, sched: Treat Intel SNC topology as default, COD as exception

[Alison Schofield <alison.schofield@intel.com>]

Commit 1340ccfa9a9a ("x86,sched: Allow topologies where NUMA nodes
share an LLC") added a vendor and model specific check to never
call topology_sane() for Intel Skylake Server systems where NUMA
nodes share an LLC.

Intel Ice Lake and Sapphire Rapids CPUs also enumerate an LLC that is
shared by multiple NUMA nodes. The LLC on these CPUs is shared for
off-package data access but private to the NUMA node for on-package
access. Rather than managing a list of allowable SNC topologies, make
this SNC topology the default, and treat Intel's Cluster-On-Die (COD)
topology as the exception.

In SNC mode, Sky Lake, Ice Lake, and Sapphire Rapids servers do not
emit this warning:

sched: CPU #3's llc-sibling CPU #0 is not on the same node! [node: 1 != 0]. Ignoring dependency.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Cc: stable@vger.kernel.org
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: brice.goglin@gmail.com
---

Changes v2->v3:
- This is a v3 of this patch: https://lore.kernel.org/lkml/20210216195804.24204-1-alison.schofield@intel.com/
- Implemented PeterZ suggestion, and his code, to check for COD instead
  of SNC.
- Updated commit message and log.
- Added 'Cc stable.

Changes v1->v2:
- Implemented the minimal required change of adding the new models to
  the existing vendor and model specific check.

- Side effect of going minimalist: no longer labelled an X86_BUG (TonyL)

- Considered PeterZ suggestion of checking for COD CPUs, rather than
  SNC CPUs. That meant this snc_cpu list would go away, and so it never
  needs updating. That ups the stakes for this patch wrt LOC changed
  and testing needed. It actually drove me back to this simplest soln.

- Considered DaveH suggestion to remove the check altogether and recognize
  these topologies as sane. Not running with that further here. This patch
  is what is needed now. The broader discussion of sane topologies can
  carry on independent of this update.

- Updated commit message and log.


 arch/x86/kernel/smpboot.c | 90 ++++++++++++++++++++-------------------
 1 file changed, 46 insertions(+), 44 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 02813a7f3a7c..147b2f3a2a09 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -458,29 +458,52 @@ static bool match_smt(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
 	return false;
 }
 
+static bool match_die(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
+{
+	if (c->phys_proc_id == o->phys_proc_id &&
+	    c->cpu_die_id == o->cpu_die_id)
+		return true;
+	return false;
+}
+
+/*
+ * Unlike the other levels, we do not enforce keeping a
+ * multicore group inside a NUMA node.  If this happens, we will
+ * discard the MC level of the topology later.
+ */
+static bool match_pkg(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
+{
+	if (c->phys_proc_id == o->phys_proc_id)
+		return true;
+	return false;
+}
+
 /*
- * Define snc_cpu[] for SNC (Sub-NUMA Cluster) CPUs.
+ * Define intel_cod_cpu[] for Intel COD (Cluster-on-Die) CPUs.
  *
- * These are Intel CPUs that enumerate an LLC that is shared by
- * multiple NUMA nodes. The LLC on these systems is shared for
- * off-package data access but private to the NUMA node (half
- * of the package) for on-package access.
+ * Any Intel CPU that has multiple nodes per package and does not
+ * match intel_cod_cpu[] has the SNC (Sub-NUMA Cluster) topology.
  *
- * CPUID (the source of the information about the LLC) can only
- * enumerate the cache as being shared *or* unshared, but not
- * this particular configuration. The CPU in this case enumerates
- * the cache to be shared across the entire package (spanning both
- * NUMA nodes).
+ * When in SNC mode, these CPUs enumerate an LLC that is shared
+ * by multiple NUMA nodes. The LLC is shared for off-package data
+ * access but private to the NUMA node (half of the package) for
+ * on-package access. CPUID (the source of the information about
+ * the LLC) can only enumerate the cache as shared or unshared,
+ * but not this particular configuration.
  */
 
-static const struct x86_cpu_id snc_cpu[] = {
-	X86_MATCH_INTEL_FAM6_MODEL(SKYLAKE_X, NULL),
+static const struct x86_cpu_id intel_cod_cpu[] = {
+	X86_MATCH_INTEL_FAM6_MODEL(HASWELL_X, 0),	/* COD */
+	X86_MATCH_INTEL_FAM6_MODEL(BROADWELL_X, 0),	/* COD */
+	X86_MATCH_INTEL_FAM6_MODEL(ANY, 1),		/* SNC */
 	{}
 };
 
 static bool match_llc(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
 {
+	const struct x86_cpu_id *id = x86_match_cpu(intel_cod_cpu);
 	int cpu1 = c->cpu_index, cpu2 = o->cpu_index;
+	bool intel_snc = id && id->driver_data;
 
 	/* Do not match if we do not have a valid APICID for cpu: */
 	if (per_cpu(cpu_llc_id, cpu1) == BAD_APICID)
@@ -495,32 +518,12 @@ static bool match_llc(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
 	 * means 'c' does not share the LLC of 'o'. This will be
 	 * reflected to userspace.
 	 */
-	if (!topology_same_node(c, o) && x86_match_cpu(snc_cpu))
+	if (match_pkg(c, o) && !topology_same_node(c, o) && intel_snc)
 		return false;
 
 	return topology_sane(c, o, "llc");
 }
 
-/*
- * Unlike the other levels, we do not enforce keeping a
- * multicore group inside a NUMA node.  If this happens, we will
- * discard the MC level of the topology later.
- */
-static bool match_pkg(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
-{
-	if (c->phys_proc_id == o->phys_proc_id)
-		return true;
-	return false;
-}
-
-static bool match_die(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
-{
-	if ((c->phys_proc_id == o->phys_proc_id) &&
-		(c->cpu_die_id == o->cpu_die_id))
-		return true;
-	return false;
-}
-
 
 #if defined(CONFIG_SCHED_SMT) || defined(CONFIG_SCHED_MC)
 static inline int x86_sched_itmt_flags(void)
@@ -592,14 +595,23 @@ void set_cpu_sibling_map(int cpu)
 	for_each_cpu(i, cpu_sibling_setup_mask) {
 		o = &cpu_data(i);
 
+		if (match_pkg(c, o) && !topology_same_node(c, o))
+			x86_has_numa_in_package = true;
+
 		if ((i == cpu) || (has_smt && match_smt(c, o)))
 			link_mask(topology_sibling_cpumask, cpu, i);
 
 		if ((i == cpu) || (has_mp && match_llc(c, o)))
 			link_mask(cpu_llc_shared_mask, cpu, i);
 
+		if ((i == cpu) || (has_mp && match_die(c, o)))
+			link_mask(topology_die_cpumask, cpu, i);
 	}
 
+	threads = cpumask_weight(topology_sibling_cpumask(cpu));
+	if (threads > __max_smt_threads)
+		__max_smt_threads = threads;
+
 	/*
 	 * This needs a separate iteration over the cpus because we rely on all
 	 * topology_sibling_cpumask links to be set-up.
@@ -613,8 +625,7 @@ void set_cpu_sibling_map(int cpu)
 			/*
 			 *  Does this new cpu bringup a new core?
 			 */
-			if (cpumask_weight(
-			    topology_sibling_cpumask(cpu)) == 1) {
+			if (threads == 1) {
 				/*
 				 * for each core in package, increment
 				 * the booted_cores for this new cpu
@@ -631,16 +642,7 @@ void set_cpu_sibling_map(int cpu)
 			} else if (i != cpu && !c->booted_cores)
 				c->booted_cores = cpu_data(i).booted_cores;
 		}
-		if (match_pkg(c, o) && !topology_same_node(c, o))
-			x86_has_numa_in_package = true;
-
-		if ((i == cpu) || (has_mp && match_die(c, o)))
-			link_mask(topology_die_cpumask, cpu, i);
 	}
-
-	threads = cpumask_weight(topology_sibling_cpumask(cpu));
-	if (threads > __max_smt_threads)
-		__max_smt_threads = threads;
 }
 
 /* maps the cpu to the sched domain representing multi-core */
-- 
2.20.1