rtla/timerlat_bpf: Allow resuming tracing

Currently, rtla-timerlat BPF program uses a global variable stored in a
.bss section to store whether tracing has been stopped.

Move the information to a separate map, so that it is easily writable
from userspace, and add a function that clears the value, resuming
tracing after it has been stopped.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Chang Yin <cyin@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Cc: Crystal Wood <crwood@redhat.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/20250626123405.1496931-4-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/tools/tracing/rtla/src/timerlat.bpf.c b/tools/tracing/rtla/src/timerlat.bpf.c
index 96196d46e1701e3dab8f8519913a5a5a7a370040..084cd10c21fc4991ef518247f9989d52989f0919 100644 (file)
--- a/tools/tracing/rtla/src/timerlat.bpf.c
+++ b/tools/tracing/rtla/src/timerlat.bpf.c
@@ -28,6 +28,13 @@ struct {
        __type(value, unsigned long long);
 } summary_irq SEC(".maps"), summary_thread SEC(".maps"), summary_user SEC(".maps");
 
+struct {
+       __uint(type, BPF_MAP_TYPE_ARRAY);
+       __uint(max_entries, 1);
+       __type(key, unsigned int);
+       __type(value, unsigned long long);
+} stop_tracing SEC(".maps");
+
 struct {
        __uint(type, BPF_MAP_TYPE_RINGBUF);
        __uint(max_entries, 1);
@@ -41,8 +48,6 @@ const volatile int irq_threshold;
 const volatile int thread_threshold;
 const volatile bool aa_only;
 
-int stop_tracing;
-
 nosubprog unsigned long long map_get(void *map,
                                     unsigned int key)
 {
@@ -109,7 +114,7 @@ nosubprog void set_stop_tracing(void)
        int value = 0;
 
        /* Suppress further sample processing */
-       stop_tracing = 1;
+       map_set(&stop_tracing, 0, 1);
 
        /* Signal to userspace */
        bpf_ringbuf_output(&signal_stop_tracing, &value, sizeof(value), 0);
@@ -121,7 +126,7 @@ int handle_timerlat_sample(struct trace_event_raw_timerlat_sample *tp_args)
        unsigned long long latency, latency_us;
        int bucket;
 
-       if (stop_tracing)
+       if (map_get(&stop_tracing, 0))
                return 0;
 
        latency = tp_args->timer_latency / output_divisor;

diff --git a/tools/tracing/rtla/src/timerlat_bpf.c b/tools/tracing/rtla/src/timerlat_bpf.c
index 0bc44ce5d69bd9d7d42e6c75402bda8c353fbf0f..1666215dd687b8912a9f3cc905d9ae65a14134f7 100644 (file)
--- a/tools/tracing/rtla/src/timerlat_bpf.c
+++ b/tools/tracing/rtla/src/timerlat_bpf.c
@@ -106,6 +106,19 @@ int timerlat_bpf_wait(int timeout)
        return retval;
 }
 
+/*
+ * timerlat_bpf_restart_tracing - restart stopped tracing
+ */
+int timerlat_bpf_restart_tracing(void)
+{
+       unsigned int key = 0;
+       unsigned long long value = 0;
+
+       return bpf_map__update_elem(bpf->maps.stop_tracing,
+                                   &key, sizeof(key),
+                                   &value, sizeof(value), BPF_ANY);
+}
+
 static int get_value(struct bpf_map *map_irq,
                     struct bpf_map *map_thread,
                     struct bpf_map *map_user,

diff --git a/tools/tracing/rtla/src/timerlat_bpf.h b/tools/tracing/rtla/src/timerlat_bpf.h
index f1b54dbddb0e2f748b7457af87a6dc1c60a853cd..118487436d3048e0dff935df82f7e84624098944 100644 (file)
--- a/tools/tracing/rtla/src/timerlat_bpf.h
+++ b/tools/tracing/rtla/src/timerlat_bpf.h
@@ -18,6 +18,7 @@ int timerlat_bpf_attach(void);
 void timerlat_bpf_detach(void);
 void timerlat_bpf_destroy(void);
 int timerlat_bpf_wait(int timeout);
+int timerlat_bpf_restart_tracing(void);
 int timerlat_bpf_get_hist_value(int key,
                                long long *value_irq,
                                long long *value_thread,
@@ -28,6 +29,7 @@ int timerlat_bpf_get_summary_value(enum summary_field key,
                                   long long *value_thread,
                                   long long *value_user,
                                   int cpus);
+
 static inline int have_libbpf_support(void) { return 1; }
 #else
 static inline int timerlat_bpf_init(struct timerlat_params *params)
@@ -38,6 +40,7 @@ static inline int timerlat_bpf_attach(void) { return -1; }
 static inline void timerlat_bpf_detach(void) { };
 static inline void timerlat_bpf_destroy(void) { };
 static inline int timerlat_bpf_wait(int timeout) { return -1; }
+static inline int timerlat_bpf_restart_tracing(void) { return -1; };
 static inline int timerlat_bpf_get_hist_value(int key,
                                              long long *value_irq,
                                              long long *value_thread,