[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <20241021071304.27856-1-arighi@nvidia.com>
Date: Mon, 21 Oct 2024 09:13:04 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
David Vernet <void@...ifault.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] sched_ext: introduce LLC awareness to the default idle selection policy
Rely on the scheduler topology information to implement basic LLC
awareness in the sched_ext build-in idle selection policy.
This allows schedulers using the built-in policy to make more informed
decisions when selecting an idle CPU in systems with multiple LLCs, such
as NUMA systems or chiplet-based architectures, and it helps keep tasks
within the same LLC domain, thereby improving cache locality.
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
kernel/sched/ext.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index a13a6461a290..a301c4d7d49f 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -874,6 +874,14 @@ static struct scx_exit_info *scx_exit_info;
static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0);
static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0);
+#ifdef CONFIG_SMP
+/*
+ * Per-CPU cpumasks used by the built-in idle CPU selection policy to determine
+ * task's LLC domain.
+ */
+static DEFINE_PER_CPU(cpumask_var_t, select_cpu_mask);
+#endif /* CONFIG_SMP */
+
/*
* A monotically increasing sequence number that is incremented every time a
* scheduler is enabled. This can be used by to check if any custom sched_ext
@@ -3122,6 +3130,8 @@ static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
u64 wake_flags, bool *found)
{
+ struct cpumask *llc_cpus = this_cpu_cpumask_var_ptr(select_cpu_mask);
+ struct sched_domain *sd;
s32 cpu;
*found = false;
@@ -3168,27 +3178,62 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
}
}
+ /*
+ * Determine the task's LLC domain.
+ */
+ sd = rcu_dereference(per_cpu(sd_llc, prev_cpu));
+ if (sd)
+ cpumask_and(llc_cpus, sched_domain_span(sd), p->cpus_ptr);
+ else
+ cpumask_copy(llc_cpus, p->cpus_ptr);
+
/*
* If CPU has SMT, any wholly idle CPU is likely a better pick than
* partially idle @prev_cpu.
*/
if (sched_smt_active()) {
+ /*
+ * Keep using @prev_cpu if it's part of a fully idle core.
+ */
if (cpumask_test_cpu(prev_cpu, idle_masks.smt) &&
test_and_clear_cpu_idle(prev_cpu)) {
cpu = prev_cpu;
goto cpu_found;
}
+ /*
+ * Search for any fully idle core in the same LLC domain.
+ */
+ cpu = scx_pick_idle_cpu(llc_cpus, SCX_PICK_IDLE_CORE);
+ if (cpu >= 0)
+ goto cpu_found;
+
+ /*
+ * Search for any full idle core usable by the task.
+ */
cpu = scx_pick_idle_cpu(p->cpus_ptr, SCX_PICK_IDLE_CORE);
if (cpu >= 0)
goto cpu_found;
}
+ /*
+ * Use @prev_cpu if it's idle.
+ */
if (test_and_clear_cpu_idle(prev_cpu)) {
cpu = prev_cpu;
goto cpu_found;
}
+ /*
+ * Search for any idle CPU in the same LLC domain.
+ */
+ cpu = scx_pick_idle_cpu(llc_cpus, 0);
+ if (cpu >= 0)
+ goto cpu_found;
+
+ /*
+ * Search for any idle CPU usable by the task.
+ */
cpu = scx_pick_idle_cpu(p->cpus_ptr, 0);
if (cpu >= 0)
goto cpu_found;
@@ -7189,6 +7234,19 @@ static const struct btf_kfunc_id_set scx_kfunc_set_any = {
.set = &scx_kfunc_ids_any,
};
+#ifdef CONFIG_SMP
+static void init_select_cpu_mask(void)
+{
+ int i;
+
+ for_each_possible_cpu(i)
+ zalloc_cpumask_var_node(&per_cpu(select_cpu_mask, i),
+ GFP_KERNEL, cpu_to_node(i));
+}
+#else
+static inline void init_select_cpu_mask(void) {}
+#endif /* CONFIG_SMP */
+
static int __init scx_init(void)
{
int ret;
@@ -7250,6 +7308,8 @@ static int __init scx_init(void)
return ret;
}
+ init_select_cpu_mask();
+
return 0;
}
__initcall(scx_init);
--
2.47.0
Powered by blists - more mailing lists