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scx_central: Implement fallback for missing BPF_F_TIMER_CPU_PIN support #5

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Merged
merged 1 commit into from
Dec 6, 2023
Merged

scx_central: Implement fallback for missing BPF_F_TIMER_CPU_PIN support #5

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21 changes: 19 additions & 2 deletions scheds/kernel-examples/scx_central.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,7 @@ const volatile s32 central_cpu;
const volatile u32 nr_cpu_ids = 1; /* !0 for veristat, set during init */
const volatile u64 slice_ns = SCX_SLICE_DFL;

bool timer_pinned = true;
u64 nr_total, nr_locals, nr_queued, nr_lost_pids;
u64 nr_timers, nr_dispatches, nr_mismatches, nr_retries;
u64 nr_overflows;
Expand Down Expand Up @@ -255,7 +256,7 @@ static int central_timerfn(void *map, int *key, struct bpf_timer *timer)
s32 i, curr_cpu;

curr_cpu = bpf_get_smp_processor_id();
if (curr_cpu != central_cpu) {
if (timer_pinned && (curr_cpu != central_cpu)) {
scx_bpf_error("Central timer ran on CPU %d, not central CPU %d",
curr_cpu, central_cpu);
return 0;
Expand Down Expand Up @@ -308,12 +309,28 @@ int BPF_STRUCT_OPS_SLEEPABLE(central_init)
if (!timer)
return -ESRCH;

if (bpf_get_smp_processor_id() != central_cpu)
if (bpf_get_smp_processor_id() != central_cpu) {
scx_bpf_error("init from non-central CPU");
return -EINVAL;
}

bpf_timer_init(timer, &central_timer, CLOCK_MONOTONIC);
bpf_timer_set_callback(timer, central_timerfn);

ret = bpf_timer_start(timer, TIMER_INTERVAL_NS, BPF_F_TIMER_CPU_PIN);
/*
* BPF_F_TIMER_CPU_PIN is pretty new (>=6.7). If we're running in a
* kernel which doesn't have it, bpf_timer_start() will return -EINVAL.
* Retry without the PIN. This would be the perfect use case for
* bpf_core_enum_value_exists() but the enum type doesn't have a name
* and can't be used with bpf_core_enum_value_exists(). Oh well...
*/
if (ret == -EINVAL) {
timer_pinned = false;
ret = bpf_timer_start(timer, TIMER_INTERVAL_NS, 0);
}
if (ret)
scx_bpf_error("bpf_timer_start failed (%d)", ret);
return ret;
}

Expand Down
3 changes: 3 additions & 0 deletions scheds/kernel-examples/scx_central.c
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,9 @@ int main(int argc, char **argv)
link = bpf_map__attach_struct_ops(skel->maps.central_ops);
SCX_BUG_ON(!link, "Failed to attach struct_ops");

if (!skel->data->timer_pinned)
printf("WARNING : BPF_F_TIMER_CPU_PIN not available, timer not pinned to central\n");

while (!exit_req && !uei_exited(&skel->bss->uei)) {
printf("[SEQ %llu]\n", seq++);
printf("total :%10lu local:%10lu queued:%10lu lost:%10lu\n",
Expand Down