From 7b0888b7cc1924b74ce660e02f6211df8dd46e7b Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 18 Jun 2024 10:09:20 -1000 Subject: sched_ext: Implement core-sched support The core-sched support is composed of the following parts: - task_struct->scx.core_sched_at is added. This is a timestamp which can be used to order tasks. Depending on whether the BPF scheduler implements custom ordering, it tracks either global FIFO ordering of all tasks or local-DSQ ordering within the dispatched tasks on a CPU. - prio_less() is updated to call scx_prio_less() when comparing SCX tasks. scx_prio_less() calls ops.core_sched_before() if available or uses the core_sched_at timestamp. For global FIFO ordering, the BPF scheduler doesn't need to do anything. Otherwise, it should implement ops.core_sched_before() which reflects the ordering. - When core-sched is enabled, balance_scx() balances all SMT siblings so that they all have tasks dispatched if necessary before pick_task_scx() is called. pick_task_scx() picks between the current task and the first dispatched task on the local DSQ based on availability and the core_sched_at timestamps. Note that FIFO ordering is expected among the already dispatched tasks whether running or on the local DSQ, so this path always compares core_sched_at instead of calling into ops.core_sched_before(). qmap_core_sched_before() is added to scx_qmap. It scales the distances from the heads of the queues to compare the tasks across different priority queues and seems to behave as expected. v3: Fixed build error when !CONFIG_SCHED_SMT reported by Andrea Righi. v2: Sched core added the const qualifiers to prio_less task arguments. Explicitly drop them for ops.core_sched_before() task arguments. BPF enforces access control through the verifier, so the qualifier isn't actually operative and only gets in the way when interacting with various helpers. Signed-off-by: Tejun Heo Reviewed-by: David Vernet Reviewed-by: Josh Don Cc: Andrea Righi --- kernel/Kconfig.preempt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/Kconfig.preempt') diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 39ecfc2b5a1c..7dde5e424ac3 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -135,7 +135,7 @@ config SCHED_CORE config SCHED_CLASS_EXT bool "Extensible Scheduling Class" - depends on BPF_SYSCALL && BPF_JIT && !SCHED_CORE + depends on BPF_SYSCALL && BPF_JIT help This option enables a new scheduler class sched_ext (SCX), which allows scheduling policies to be implemented as BPF programs to -- cgit v1.2.3