Commit 8cd0f08a authored by Tomas Glozar's avatar Tomas Glozar
Browse files

rtla/timerlat: Support tail call from BPF program 

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.

Link: https://lore.kernel.org/r/20251126144205.331954-2-tglozar@redhat.com


Signed-off-by: default avatarTomas Glozar <tglozar@redhat.com>
parent a08e012e

tools/tracing/rtla/src/timerlat.bpf.c

+21 −4
Original line number Diff line number Diff line
@@ -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")
@@ -138,19 +155,19 @@ 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);



		if (thread_threshold != 0 && latency_us >= thread_threshold)

			set_stop_tracing();

			set_stop_tracing(tp_args);

	}



	return 0;

tools/tracing/rtla/src/timerlat_bpf.c

+13 −0
Original line number Diff line number Diff line
@@ -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);

}



/*

 * timerlat_bpf_attach - attach BPF program to collect timerlat data

 */

tools/tracing/rtla/src/timerlat_bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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);