From 59674fc9d0bfd96ce8a776680ee1cf22c28c9ac7 Mon Sep 17 00:00:00 2001 From: Tony Luck Date: Tue, 3 Mar 2026 11:55:44 +0100 Subject: [PATCH] x86/resctrl: Fix SNC detection Now that the x86 topology code has a sensible nodes-per-package measure, that does not depend on the online status of CPUs, use this to divinate the SNC mode. Note that when Cluster on Die (CoD) is configured on older systems this will also show multiple NUMA nodes per package. Intel Resource Director Technology is incomaptible with CoD. Print a warning and do not use the fixup MSR_RMID_SNC_CONFIG. Signed-off-by: Tony Luck Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ingo Molnar Tested-by: Zhang Rui Tested-by: Chen Yu Link: https://patch.msgid.link/aaCxbbgjL6OZ6VMd@agluck-desk3 Link: https://patch.msgid.link/20260303110100.367976706@infradead.org --- arch/x86/kernel/cpu/resctrl/monitor.c | 36 ++++----------------------- 1 file changed, 5 insertions(+), 31 deletions(-) diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c index e6a154240b8d..9bd87bae4983 100644 --- a/arch/x86/kernel/cpu/resctrl/monitor.c +++ b/arch/x86/kernel/cpu/resctrl/monitor.c @@ -364,7 +364,7 @@ void arch_mon_domain_online(struct rdt_resource *r, struct rdt_l3_mon_domain *d) msr_clear_bit(MSR_RMID_SNC_CONFIG, 0); } -/* CPU models that support MSR_RMID_SNC_CONFIG */ +/* CPU models that support SNC and MSR_RMID_SNC_CONFIG */ static const struct x86_cpu_id snc_cpu_ids[] __initconst = { X86_MATCH_VFM(INTEL_ICELAKE_X, 0), X86_MATCH_VFM(INTEL_SAPPHIRERAPIDS_X, 0), @@ -375,40 +375,14 @@ static const struct x86_cpu_id snc_cpu_ids[] __initconst = { {} }; -/* - * There isn't a simple hardware bit that indicates whether a CPU is running - * in Sub-NUMA Cluster (SNC) mode. Infer the state by comparing the - * number of CPUs sharing the L3 cache with CPU0 to the number of CPUs in - * the same NUMA node as CPU0. - * It is not possible to accurately determine SNC state if the system is - * booted with a maxcpus=N parameter. That distorts the ratio of SNC nodes - * to L3 caches. It will be OK if system is booted with hyperthreading - * disabled (since this doesn't affect the ratio). - */ static __init int snc_get_config(void) { - struct cacheinfo *ci = get_cpu_cacheinfo_level(0, RESCTRL_L3_CACHE); - const cpumask_t *node0_cpumask; - int cpus_per_node, cpus_per_l3; - int ret; + int ret = topology_num_nodes_per_package(); - if (!x86_match_cpu(snc_cpu_ids) || !ci) + if (ret > 1 && !x86_match_cpu(snc_cpu_ids)) { + pr_warn("CoD enabled system? Resctrl not supported\n"); return 1; - - cpus_read_lock(); - if (num_online_cpus() != num_present_cpus()) - pr_warn("Some CPUs offline, SNC detection may be incorrect\n"); - cpus_read_unlock(); - - node0_cpumask = cpumask_of_node(cpu_to_node(0)); - - cpus_per_node = cpumask_weight(node0_cpumask); - cpus_per_l3 = cpumask_weight(&ci->shared_cpu_map); - - if (!cpus_per_node || !cpus_per_l3) - return 1; - - ret = cpus_per_l3 / cpus_per_node; + } /* sanity check: Only valid results are 1, 2, 3, 4, 6 */ switch (ret) {