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Date: Wed, 22 May 2024 14:26:48 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, Maciej
Wieczor-Retman <maciej.wieczor-retman@...el.com>, Peter Newman
<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
<Dave.Martin@....com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
<patches@...ts.linux.dev>
Subject: Re: [PATCH v18 16/17] x86/resctrl: Sub NUMA Cluster detection and
enable
Hi Tony,
On 5/15/2024 3:23 PM, Tony Luck wrote:
> 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
Sometimes it is "Sub-NUMA Cluster" and sometimes it is "Sub NUMA Cluster".
> number CPUs sharing the L3 cache with CPU0 to the number of CPUs in
> the same NUMA node as CPU0.
>
> When SNC mode is detected, reconfigure the RMID counters by updating
> the MSR_RMID_SNC_CONFIG MSR on each socket as CPUs are seen.
>
> Clearing bit zero of the MSR divides the RMIDs and renumbers the ones
> on the second SNC node to start from zero.
>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
> arch/x86/include/asm/msr-index.h | 1 +
> arch/x86/kernel/cpu/resctrl/core.c | 104 +++++++++++++++++++++++++++++
> 2 files changed, 105 insertions(+)
>
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index e022e6eb766c..3cb8dd6311c3 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -1164,6 +1164,7 @@
> #define MSR_IA32_QM_CTR 0xc8e
> #define MSR_IA32_PQR_ASSOC 0xc8f
> #define MSR_IA32_L3_CBM_BASE 0xc90
> +#define MSR_RMID_SNC_CONFIG 0xca0
> #define MSR_IA32_L2_CBM_BASE 0xd10
> #define MSR_IA32_MBA_THRTL_BASE 0xd50
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index dd40c998df72..195f9e29c553 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -21,6 +21,7 @@
> #include <linux/err.h>
> #include <linux/cacheinfo.h>
> #include <linux/cpuhotplug.h>
> +#include <linux/mod_devicetable.h>
>
> #include <asm/cpu_device_id.h>
> #include <asm/resctrl.h>
> @@ -753,11 +754,42 @@ static void clear_closid_rmid(int cpu)
> RESCTRL_RESERVED_CLOSID);
> }
>
> +/*
> + * The power-on reset value of MSR_RMID_SNC_CONFIG is 0x1
> + * which indicates that RMIDs are configured in legacy mode.
> + * This mode is incompatible with Linux resctrl semantics
> + * as RMIDs are partitioned between SNC nodes, which requires
> + * a user to know which RMID is allocated to a task.
> + * Clearing bit 0 reconfigures the RMID counters for use
> + * in Sub NUMA Cluster mode. This mode is better for Linux.
> + * The RMID space is divided between all SNC nodes with the
> + * RMIDs renumbered to start from zero in each node when
> + * couning operations from tasks. Code to read the counters
couning -> counting
> + * must adjust RMID counter numbers based on SNC node. See
> + * __rmid_read() for code that does this.
> + */
> +static void snc_remap_rmids(int cpu)
> +{
> + u64 val;
> +
> + /* Only need to enable once per package. */
> + if (cpumask_first(topology_core_cpumask(cpu)) != cpu)
> + return;
> +
> + rdmsrl(MSR_RMID_SNC_CONFIG, val);
> + val &= ~BIT_ULL(0);
> + wrmsrl(MSR_RMID_SNC_CONFIG, val);
> +}
> +
> static int resctrl_arch_online_cpu(unsigned int cpu)
> {
> struct rdt_resource *r;
>
> mutex_lock(&domain_list_lock);
> +
> + if (snc_nodes_per_l3_cache > 1)
> + snc_remap_rmids(cpu);
> +
> for_each_capable_rdt_resource(r)
> domain_add_cpu(cpu, r);
> mutex_unlock(&domain_list_lock);
> @@ -997,11 +1029,83 @@ static __init bool get_rdt_resources(void)
> return (rdt_mon_capable || rdt_alloc_capable);
> }
>
> +/* CPU models that support 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),
> + X86_MATCH_VFM(INTEL_EMERALDRAPIDS_X, 0),
> + X86_MATCH_VFM(INTEL_GRANITERAPIDS_X, 0),
> + X86_MATCH_VFM(INTEL_ATOM_CRESTMONT_X, 0),
> + {}
> +};
> +
> +/*
> + * 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 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 cpu_cacheinfo *ci = get_cpu_cacheinfo(0);
> + const cpumask_t *node0_cpumask;
> + cpumask_t *l3_cpumask = NULL;
> + int i, ret;
> +
> + if (!x86_match_cpu(snc_cpu_ids))
> + 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();
> +
> + for (i = 0; i < ci->num_leaves; i++) {
> + if (ci->info_list[i].level == 3) {
> + if (ci->info_list[i].attributes & CACHE_ID) {
> + l3_cpumask = &ci->info_list[i].shared_cpu_map;
> + break;
> + }
> + }
> + }
> + if (!l3_cpumask) {
> + pr_info("can't get CPU0 L3 mask\n");
Sentence can start with upper case
> + return 1;
> + }
> +
> + node0_cpumask = cpumask_of_node(cpu_to_node(0));
> +
> + ret = bitmap_weight(cpumask_bits(l3_cpumask), nr_cpu_ids) /
> + bitmap_weight(cpumask_bits(node0_cpumask), nr_cpu_ids);
> +
Can cpumask_weight() be used?
> + /* sanity check: Only valid results are 1, 2, 3, 4 */
> + switch (ret) {
> + case 1:
> + break;
> + case 2 ... 4:
> + pr_info("Sub-NUMA cluster detected with %d nodes per L3 cache\n", ret);
> + rdt_resources_all[RDT_RESOURCE_L3].r_resctrl.mon_scope = RESCTRL_NODE;
> + break;
> + default:
> + pr_warn("Ignore improbable SNC node count %d\n", ret);
> + ret = 1;
> + break;
> + }
> +
> + return ret;
> +}
> +
> static __init void rdt_init_res_defs_intel(void)
> {
> struct rdt_hw_resource *hw_res;
> struct rdt_resource *r;
>
> + snc_nodes_per_l3_cache = snc_get_config();
> +
> for_each_rdt_resource(r) {
> hw_res = resctrl_to_arch_res(r);
>
Reinette
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