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Date: Thu, 10 Mar 2022 15:18:51 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Qing Wang <wangqing@...o.com>
Cc: Catalin Marinas <Catalin.Marinas@....com>,
Will Deacon <will@...nel.org>,
Sudeep Holla <sudeep.holla@....com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: topology: make cache topology separate from cpu topology
On Thu, 10 Mar 2022 at 13:59, Qing Wang <wangqing@...o.com> wrote:
>
> From: Wang Qing <wangqing@...o.com>
>
> Some architectures(e.g. ARM64), caches are implemented below:
> cluster: ****** cluster 0 ***** ****** cluster 1 *****
> core: 0 1 2 3 4 5 6 7
> cache(Leveln): **cache0** **cache1** **cache2** **cache3**
> sd_llc_id(current): 0 0 0 0 4 4 4 4
> sd_llc_id(should be): 0 0 2 2 4 4 6 6
>
> Caches and cpus have different topology, this causes cpus_share_cache()
> return the wrong value, which will affect the CPU load balance.
What does your current scheduler topology look like?
For CPU 0 to 3, do you have the below ?
DIE [0 - 3] [4-7]
MC [0] [1] [2] [3]
But you would like something like below for cpu 0-1 instead ?
DIE [0 - 3] [4-7]
CLS [0 - 1] [2 - 3]
MC [0] [1]
with SD_SHARE_PKG_RESOURCES only set to MC level ?
>
> Cache topology should be separated with CPU topology, it can be obtained
> from "next-level-cache" in DTS preferentially.
>
> Signed-off-by: Wang Qing <wangqing@...o.com>
> ---
> arch/arm64/kernel/smp.c | 1 +
> drivers/base/arch_topology.c | 23 +++++++++++++++++++++++
> include/linux/arch_topology.h | 3 +++
> kernel/sched/topology.c | 33 +++++++++++++++++++++++++++++++--
> 4 files changed, 58 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 27df5c1..94cf649
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -723,6 +723,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
> unsigned int this_cpu;
>
> init_cpu_topology();
> + init_cpu_cache_topology();
>
> this_cpu = smp_processor_id();
> store_cpu_topology(this_cpu);
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 9761541..613213f
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -613,6 +613,7 @@ static int __init parse_dt_topology(void)
> */
> struct cpu_topology cpu_topology[NR_CPUS];
> EXPORT_SYMBOL_GPL(cpu_topology);
> +struct device_node *cache_topology[NR_CPUS][MAX_CPU_CACHE_LEVEL];
AFAICT, arch_topology.c is only used by arm/arm64 and riscv so this is
not initialized for other archs
>
> const struct cpumask *cpu_coregroup_mask(int cpu)
> {
> @@ -738,4 +739,26 @@ void __init init_cpu_topology(void)
> else if (of_have_populated_dt() && parse_dt_topology())
> reset_cpu_topology();
> }
> +
> +void __init init_cpu_cache_topology(void)
> +{
> + struct device_node *node_cpu, *node_cache;
> + int cpu, level;
> +
> + for_each_possible_cpu(cpu) {
> + node_cpu = of_get_cpu_node(cpu, NULL);
> + if (!node_cpu)
> + continue;
> +
> + level = 0;
> + node_cache = node_cpu;
> + while (level < MAX_CPU_CACHE_LEVEL) {
> + node_cache = of_parse_phandle(node_cache, "next-level-cache", 0);
> + if (!node_cache)
> + break;
> + cache_topology[cpu][level++] = node_cache;
> + }
> + of_node_put(node_cpu);
> + }
> +}
> #endif
> diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> index cce6136b..d37f47d
> --- a/include/linux/arch_topology.h
> +++ b/include/linux/arch_topology.h
> @@ -72,6 +72,8 @@ struct cpu_topology {
> };
>
> #ifdef CONFIG_GENERIC_ARCH_TOPOLOGY
> +#define MAX_CPU_CACHE_LEVEL 7
> +extern struct device_node *cache_topology[NR_CPUS][MAX_CPU_CACHE_LEVEL];
> extern struct cpu_topology cpu_topology[NR_CPUS];
>
> #define topology_physical_package_id(cpu) (cpu_topology[cpu].package_id)
> @@ -82,6 +84,7 @@ extern struct cpu_topology cpu_topology[NR_CPUS];
> #define topology_cluster_cpumask(cpu) (&cpu_topology[cpu].cluster_sibling)
> #define topology_llc_cpumask(cpu) (&cpu_topology[cpu].llc_sibling)
> void init_cpu_topology(void);
> +void init_cpu_cache_topology(void);
> void store_cpu_topology(unsigned int cpuid);
> const struct cpumask *cpu_coregroup_mask(int cpu);
> const struct cpumask *cpu_clustergroup_mask(int cpu);
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index d201a70..10850d6
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -650,6 +650,36 @@ DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
> DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
>
> +static void set_sd_llc(int cpu, struct sched_domain *sd, int *first_cpu, int *cpu_num)
> +{
> + int cache_level, cpu_id;
> + int first, last;
> + int id = cpumask_first(sched_domain_span(sd));
> + int size = cpumask_weight(sched_domain_span(sd));
> +
> + *first_cpu = id;
> + *cpu_num = size;
> +
> + for (cache_level = 0; cache_level < MAX_CPU_CACHE_LEVEL; cache_level++) {
> + if (!cache_topology[cpu][cache_level])
> + break;
> +
> + first = -1;
> + last = id;
> + for (cpu_id = 0; cpu_id < NR_CPUS; cpu_id++) {
> + if (cache_topology[cpu][cache_level] == cache_topology[cpu_id][cache_level]) {
> + if (cpu_id >= id && cpu_id < id + size) {
> + first = (first == -1)?cpu_id:first;
> + last = cpu_id;
> + } else
> + return;
> + }
> + }
> + *first_cpu = first;
> + *cpu_num = last - first + 1;
> + }
> +}
> +
> static void update_top_cache_domain(int cpu)
> {
> struct sched_domain_shared *sds = NULL;
> @@ -659,8 +689,7 @@ static void update_top_cache_domain(int cpu)
>
> sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES);
> if (sd) {
> - id = cpumask_first(sched_domain_span(sd));
> - size = cpumask_weight(sched_domain_span(sd));
> + set_sd_llc(cpu, sd, &id, &size);
In scheduler, we look for the last level of SD_SHARE_PKG_RESOURCES to
find shared memory. It seems that cpu_coregroup_mask doesn't return
the correct cpumask in your case as it returns a full cluster instead
of a subset
> sds = sd->shared;
sds must stay aligned with id and size so instead of modifying id and
size you should returns a cpumask that reflects your topology
> }
>
> --
> 2.7.4
>
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