On Mon, Oct 27, 2025 at 04:33:55PM +0100, Tomas Glozar wrote:
> Add a map to the rtla-timerlat BPF program that holds a file descriptor
> of another BPF program, to be executed on threshold overflow.
>
> timerlat_bpf_set_action() is added as an interface to set the program.
>
> Signed-off-by: Tomas Glozar <[email protected]>
> ---
> tools/tracing/rtla/src/timerlat.bpf.c | 23 ++++++++++++++++++++---
> tools/tracing/rtla/src/timerlat_bpf.c | 13 +++++++++++++
> tools/tracing/rtla/src/timerlat_bpf.h | 1 +
> 3 files changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/tools/tracing/rtla/src/timerlat.bpf.c
> b/tools/tracing/rtla/src/timerlat.bpf.c
> index 084cd10c21fc..19ccd9abf8d4 100644
> --- a/tools/tracing/rtla/src/timerlat.bpf.c
> +++ b/tools/tracing/rtla/src/timerlat.bpf.c
> @@ -40,6 +40,17 @@ struct {
> __uint(max_entries, 1);
> } signal_stop_tracing SEC(".maps");
>
> +struct {
> + __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
> + __uint(key_size, sizeof(unsigned int));
> + __uint(max_entries, 1);
> + __array(values, unsigned int (void *));
> +} bpf_action SEC(".maps") = {
> + .values = {
> + [0] = 0
> + },
> +};
> +
> /* Params to be set by rtla */
> const volatile int bucket_size = 1;
> const volatile int output_divisor = 1000;
> @@ -109,7 +120,7 @@ nosubprog void update_summary(void *map,
> map_set(map, SUMMARY_SUM, map_get(map, SUMMARY_SUM) + latency);
> }
>
> -nosubprog void set_stop_tracing(void)
> +nosubprog void set_stop_tracing(struct trace_event_raw_timerlat_sample
> *tp_args)
> {
> int value = 0;
>
> @@ -118,6 +129,12 @@ nosubprog void set_stop_tracing(void)
>
> /* Signal to userspace */
> bpf_ringbuf_output(&signal_stop_tracing, &value, sizeof(value), 0);
> +
> + /*
> + * Call into BPF action program, if attached.
> + * Otherwise, just silently fail.
> + */
> + bpf_tail_call(tp_args, &bpf_action, 0);
> }
>
> SEC("tp/osnoise/timerlat_sample")
> @@ -138,13 +155,13 @@ int handle_timerlat_sample(struct
> trace_event_raw_timerlat_sample *tp_args)
> update_summary(&summary_irq, latency, bucket);
>
> if (irq_threshold != 0 && latency_us >= irq_threshold)
> - set_stop_tracing();
> + set_stop_tracing(tp_args);
> } else if (tp_args->context == 1) {
> update_main_hist(&hist_thread, bucket);
> update_summary(&summary_thread, latency, bucket);
>
> if (thread_threshold != 0 && latency_us >= thread_threshold)
> - set_stop_tracing();
> + set_stop_tracing(tp_args);
> } else {
> update_main_hist(&hist_user, bucket);
> update_summary(&summary_user, latency, bucket);
> diff --git a/tools/tracing/rtla/src/timerlat_bpf.c
> b/tools/tracing/rtla/src/timerlat_bpf.c
> index e97d16646bcd..1d619e502c65 100644
> --- a/tools/tracing/rtla/src/timerlat_bpf.c
> +++ b/tools/tracing/rtla/src/timerlat_bpf.c
> @@ -59,6 +59,19 @@ int timerlat_bpf_init(struct timerlat_params *params)
> return 0;
> }
>
> +/*
> + * timerlat_bpf_set_action - set action on threshold executed on BPF side
> + */
> +static int timerlat_bpf_set_action(struct bpf_program *prog)
> +{
> + unsigned int key = 0, value = bpf_program__fd(prog);
> +
> + return bpf_map__update_elem(bpf->maps.bpf_action,
> + &key, sizeof(key),
> + &value, sizeof(value),
> + BPF_ANY);
> +}
> +
I believe it makes more sense to add the definition of this function to
the patch where it is called.
> /*
> * timerlat_bpf_attach - attach BPF program to collect timerlat data
> */
> diff --git a/tools/tracing/rtla/src/timerlat_bpf.h
> b/tools/tracing/rtla/src/timerlat_bpf.h
> index 118487436d30..b5009092c7a3 100644
> --- a/tools/tracing/rtla/src/timerlat_bpf.h
> +++ b/tools/tracing/rtla/src/timerlat_bpf.h
> @@ -12,6 +12,7 @@ enum summary_field {
> };
>
> #ifndef __bpf__
> +#include <bpf/libbpf.h>
> #ifdef HAVE_BPF_SKEL
> int timerlat_bpf_init(struct timerlat_params *params);
> int timerlat_bpf_attach(void);
> --
> 2.51.0
>
