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sched_ext/scx_qmap: Pick idle CPU for direct dispatch on !wakeup enqueues

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Because there was no way to directly dispatch to the local DSQ of a remote
CPU from ops.enqueue(), scx_qmap skipped looking for an idle CPU on !wakeup
enqueues. This restriction was removed and sched_ext now allows
SCX_DSQ_LOCAL_ON verdicts for direct dispatches.

Factor out pick_direct_dispatch_cpu() from ops.select_cpu() and use it to
direct dispatch from ops.enqueue() on !wakeup enqueues.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Cc: Dan Schatzberg <schatzberg.dan@gmail.com>
Cc: Changwoo Min <changwoo@igalia.com>
Cc: Andrea Righi <righi.andrea@gmail.com>
This commit is contained in:
Tejun Heo 2024-07-12 08:20:33 -10:00
parent 5b26f7b920
commit 1edab907b5
2 changed files with 33 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
tools/sched_ext/scx_qmap.bpf.c
View File

@ -120,11 +120,26 @@ struct {
} cpu_ctx_stor SEC(".maps");
/* Statistics */
u64 nr_enqueued, nr_dispatched, nr_reenqueued, nr_dequeued;
u64 nr_enqueued, nr_dispatched, nr_reenqueued, nr_dequeued, nr_ddsp_from_enq;
u64 nr_core_sched_execed;
u32 cpuperf_min, cpuperf_avg, cpuperf_max;
u32 cpuperf_target_min, cpuperf_target_avg, cpuperf_target_max;
static s32 pick_direct_dispatch_cpu(struct task_struct *p, s32 prev_cpu)
{
s32 cpu;
if (p->nr_cpus_allowed == 1 ||
scx_bpf_test_and_clear_cpu_idle(prev_cpu))
return prev_cpu;
cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
if (cpu >= 0)
return cpu;
return -1;
}
s32 BPF_STRUCT_OPS(qmap_select_cpu, struct task_struct *p,
s32 prev_cpu, u64 wake_flags)
{
@ -137,17 +152,14 @@ s32 BPF_STRUCT_OPS(qmap_select_cpu, struct task_struct *p,
return -ESRCH;
}
if (p->nr_cpus_allowed == 1 ||
scx_bpf_test_and_clear_cpu_idle(prev_cpu)) {
cpu = pick_direct_dispatch_cpu(p, prev_cpu);
if (cpu >= 0) {
tctx->force_local = true;
return cpu;
} else {
return prev_cpu;
}
cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
if (cpu >= 0)
return cpu;
return prev_cpu;
}
static int weight_to_idx(u32 weight)
@ -172,6 +184,7 @@ void BPF_STRUCT_OPS(qmap_enqueue, struct task_struct *p, u64 enq_flags)
u32 pid = p->pid;
int idx = weight_to_idx(p->scx.weight);
void *ring;
s32 cpu;
if (p->flags & PF_KTHREAD) {
if (stall_kernel_nth && !(++kernel_cnt % stall_kernel_nth))
@ -207,6 +220,14 @@ void BPF_STRUCT_OPS(qmap_enqueue, struct task_struct *p, u64 enq_flags)
return;
}
/* if !WAKEUP, select_cpu() wasn't called, try direct dispatch */
if (!(enq_flags & SCX_ENQ_WAKEUP) &&
(cpu = pick_direct_dispatch_cpu(p, scx_bpf_task_cpu(p))) >= 0) {
__sync_fetch_and_add(&nr_ddsp_from_enq, 1);
scx_bpf_dispatch(p, SCX_DSQ_LOCAL_ON | cpu, slice_ns, enq_flags);
return;
}
/*
* If the task was re-enqueued due to the CPU being preempted by a
* higher priority scheduling class, just re-enqueue the task directly

5
tools/sched_ext/scx_qmap.c
View File

@ -116,10 +116,11 @@ int main(int argc, char **argv)
long nr_enqueued = skel->bss->nr_enqueued;
long nr_dispatched = skel->bss->nr_dispatched;
printf("stats : enq=%lu dsp=%lu delta=%ld reenq=%"PRIu64" deq=%"PRIu64" core=%"PRIu64"\n",
printf("stats : enq=%lu dsp=%lu delta=%ld reenq=%"PRIu64" deq=%"PRIu64" core=%"PRIu64" enq_ddsp=%"PRIu64"\n",
nr_enqueued, nr_dispatched, nr_enqueued - nr_dispatched,
skel->bss->nr_reenqueued, skel->bss->nr_dequeued,
skel->bss->nr_core_sched_execed);
skel->bss->nr_core_sched_execed,
skel->bss->nr_ddsp_from_enq);
if (__COMPAT_has_ksym("scx_bpf_cpuperf_cur"))
printf("cpuperf: cur min/avg/max=%u/%u/%u target min/avg/max=%u/%u/%u\n",
skel->bss->cpuperf_min,