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Message-ID: <Z64Y4Sgw30Pdj81J@thinkpad>
Date: Thu, 13 Feb 2025 11:08:01 -0500
From: Yury Norov <yury.norov@...il.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Valentin Schneider <vschneid@...hat.com>,
Joel Fernandes <joel@...lfernandes.org>, Ian May <ianm@...dia.com>,
bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] sched_ext: idle: Introduce
SCX_OPS_BUILTIN_IDLE_PER_NODE
On Wed, Feb 12, 2025 at 05:48:12PM +0100, Andrea Righi wrote:
> Add the new scheduler flag SCX_OPS_BUILTIN_IDLE_PER_NODE, which allows
> BPF schedulers to select between using a global flat idle cpumask or
> multiple per-node cpumasks.
>
> This only introduces the flag and the mechanism to enable/disable this
> feature without affecting any scheduling behavior.
>
> Cc: Yury Norov <yury.norov@...il.com>
> Signed-off-by: Andrea Righi <arighi@...dia.com>
> ---
> kernel/sched/ext.c | 21 ++++++++++++++++++--
> kernel/sched/ext_idle.c | 29 +++++++++++++++++++++-------
> kernel/sched/ext_idle.h | 4 ++--
> tools/sched_ext/include/scx/compat.h | 3 +++
> 4 files changed, 46 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index c47e7e2024a94..c3e154f0e8188 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -138,6 +138,12 @@ enum scx_ops_flags {
> */
> SCX_OPS_ENQ_MIGRATION_DISABLED = 1LLU << 4,
>
> + /*
> + * If set, enable per-node idle cpumasks. If clear, use a single global
> + * flat idle cpumask.
> + */
> + SCX_OPS_BUILTIN_IDLE_PER_NODE = 1LLU << 5,
> +
> /*
> * CPU cgroup support flags
> */
> @@ -148,6 +154,7 @@ enum scx_ops_flags {
> SCX_OPS_ENQ_EXITING |
> SCX_OPS_ENQ_MIGRATION_DISABLED |
> SCX_OPS_SWITCH_PARTIAL |
> + SCX_OPS_BUILTIN_IDLE_PER_NODE |
> SCX_OPS_HAS_CGROUP_WEIGHT,
> };
>
> @@ -3409,7 +3416,7 @@ static void handle_hotplug(struct rq *rq, bool online)
> atomic_long_inc(&scx_hotplug_seq);
>
> if (scx_enabled())
> - scx_idle_update_selcpu_topology();
> + scx_idle_update_selcpu_topology(&scx_ops);
>
> if (online && SCX_HAS_OP(cpu_online))
> SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_online, cpu);
> @@ -5184,6 +5191,16 @@ static int validate_ops(const struct sched_ext_ops *ops)
> return -EINVAL;
> }
>
> + /*
> + * SCX_OPS_BUILTIN_IDLE_PER_NODE requires built-in CPU idle
> + * selection policy to be enabled.
> + */
> + if ((ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) &&
> + (ops->update_idle && !(ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE))) {
> + scx_ops_error("SCX_OPS_BUILTIN_IDLE_PER_NODE requires CPU idle selection enabled");
> + return -EINVAL;
> + }
> +
> return 0;
> }
>
> @@ -5308,7 +5325,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
> static_branch_enable_cpuslocked(&scx_has_op[i]);
>
> check_hotplug_seq(ops);
> - scx_idle_update_selcpu_topology();
> + scx_idle_update_selcpu_topology(ops);
>
> cpus_read_unlock();
>
> diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
> index ed1804506585b..59b9e95238e97 100644
> --- a/kernel/sched/ext_idle.c
> +++ b/kernel/sched/ext_idle.c
> @@ -14,6 +14,9 @@
> /* Enable/disable built-in idle CPU selection policy */
> static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);
>
> +/* Enable/disable per-node idle cpumasks */
> +static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_per_node);
> +
> #ifdef CONFIG_SMP
> #ifdef CONFIG_CPUMASK_OFFSTACK
> #define CL_ALIGNED_IF_ONSTACK
> @@ -204,7 +207,7 @@ static bool llc_numa_mismatch(void)
> * CPU belongs to a single LLC domain, and that each LLC domain is entirely
> * contained within a single NUMA node.
> */
> -void scx_idle_update_selcpu_topology(void)
> +void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops)
> {
> bool enable_llc = false, enable_numa = false;
> unsigned int nr_cpus;
> @@ -237,13 +240,19 @@ void scx_idle_update_selcpu_topology(void)
> * If all CPUs belong to the same NUMA node and the same LLC domain,
> * enabling both NUMA and LLC optimizations is unnecessary, as checking
> * for an idle CPU in the same domain twice is redundant.
> + *
> + * If SCX_OPS_BUILTIN_IDLE_PER_NODE is enabled ignore the NUMA
> + * optimization, as we would naturally select idle CPUs within
> + * specific NUMA nodes querying the corresponding per-node cpumask.
> */
> - nr_cpus = numa_weight(cpu);
> - if (nr_cpus > 0) {
> - if (nr_cpus < num_online_cpus() && llc_numa_mismatch())
> - enable_numa = true;
> - pr_debug("sched_ext: NUMA=%*pb weight=%u\n",
> - cpumask_pr_args(numa_span(cpu)), numa_weight(cpu));
> + if (!(ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)) {
> + nr_cpus = numa_weight(cpu);
> + if (nr_cpus > 0) {
> + if (nr_cpus < num_online_cpus() && llc_numa_mismatch())
> + enable_numa = true;
> + pr_debug("sched_ext: NUMA=%*pb weight=%u\n",
> + cpumask_pr_args(numa_span(cpu)), numa_weight(cpu));
No need to call numa_weight(cpu) for the 2nd time, right?
> + }
> }
> rcu_read_unlock();
>
> @@ -530,6 +539,11 @@ void scx_idle_enable(struct sched_ext_ops *ops)
> }
> static_branch_enable(&scx_builtin_idle_enabled);
>
> + if (ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)
> + static_branch_enable(&scx_builtin_idle_per_node);
> + else
> + static_branch_disable(&scx_builtin_idle_per_node);
> +
> #ifdef CONFIG_SMP
> /*
> * Consider all online cpus idle. Should converge to the actual state
> @@ -543,6 +557,7 @@ void scx_idle_enable(struct sched_ext_ops *ops)
> void scx_idle_disable(void)
> {
> static_branch_disable(&scx_builtin_idle_enabled);
> + static_branch_disable(&scx_builtin_idle_per_node);
> }
>
> /********************************************************************************
> diff --git a/kernel/sched/ext_idle.h b/kernel/sched/ext_idle.h
> index bbac0fd9a5ddd..339b6ec9c4cb7 100644
> --- a/kernel/sched/ext_idle.h
> +++ b/kernel/sched/ext_idle.h
> @@ -13,12 +13,12 @@
> struct sched_ext_ops;
>
> #ifdef CONFIG_SMP
> -void scx_idle_update_selcpu_topology(void);
> +void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops);
> void scx_idle_init_masks(void);
> bool scx_idle_test_and_clear_cpu(int cpu);
> s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags);
> #else /* !CONFIG_SMP */
> -static inline void scx_idle_update_selcpu_topology(void) {}
> +static inline void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops) {}
> static inline void scx_idle_init_masks(void) {}
> static inline bool scx_idle_test_and_clear_cpu(int cpu) { return false; }
> static inline s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
> diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
> index b50280e2ba2ba..d63cf40be8eee 100644
> --- a/tools/sched_ext/include/scx/compat.h
> +++ b/tools/sched_ext/include/scx/compat.h
> @@ -109,6 +109,9 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
> #define SCX_OPS_SWITCH_PARTIAL \
> __COMPAT_ENUM_OR_ZERO("scx_ops_flags", "SCX_OPS_SWITCH_PARTIAL")
>
> +#define SCX_OPS_BUILTIN_IDLE_PER_NODE \
> + __COMPAT_ENUM_OR_ZERO("scx_ops_flags", "SCX_OPS_BUILTIN_IDLE_PER_NODE")
> +
> static inline long scx_hotplug_seq(void)
> {
> int fd;
> --
> 2.48.1
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