[DTrace-devel] [PATCH v2 dtrace 3/3] sched: fix on-cpu firing for kernels < 5.16

[Alan Maguire]

The solution for sched:::on-cpu firing (probing
__perf_event_task_sched_in) only works on 5.16 and later as
the relevant function is not in available_filter_functions
in earlier kernels.

Instead use the fbt::finish_task_switch*:return probe as this
will cover .isra.0-suffixed optimizations if they are applied
to finish_task_switch().

Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
---
 libdtrace/dt_prov_sched.c | 23 ++---------------------
 1 file changed, 2 insertions(+), 21 deletions(-)

diff --git a/libdtrace/dt_prov_sched.c b/libdtrace/dt_prov_sched.c
index 4fbd24ab..e9a1b0c9 100644
--- a/libdtrace/dt_prov_sched.c
+++ b/libdtrace/dt_prov_sched.c
@@ -28,7 +28,7 @@ static probe_dep_t	probes[] = {
 	{ "off-cpu",
 	  DTRACE_PROBESPEC_NAME,	"rawtp:sched::sched_switch" },
 	{ "on-cpu",
-	  DTRACE_PROBESPEC_NAME,	"fbt::__perf_event_task_sched_in:entry" },
+	  DTRACE_PROBESPEC_NAME,	"fbt:vmlinux:finish_task_switch*:return" },
 	{ "surrender",
 	  DTRACE_PROBESPEC_NAME,	"fbt::do_sched_yield:entry" },
 	{ "tick",
@@ -157,26 +157,7 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
  */
 static void enable(dtrace_hdl_t *dtp, dt_probe_t *prp)
 {
-	struct perf_event_attr attr = {};
-	int swfd;
-
-	if (strcmp(prp->desc->prb, "on-cpu") != 0)
-		return dt_sdt_enable(dtp, prp);
-
-	memset(&attr, 0, sizeof(attr));
-	attr.size = sizeof(attr);
-	attr.type = PERF_TYPE_SOFTWARE;
-	attr.config = PERF_COUNT_SW_CONTEXT_SWITCHES;
-	attr.freq = 1;
-	attr.sample_freq = 1000;
-	attr.context_switch = 1;
-
-	swfd = dt_perf_event_open(&attr, -1, 0, -1, 0);
-	if (swfd < 0)
-		dt_dprintf("perf event open failed for context_switch: %d\n", errno);
-	else
-		prp->prv_data = (void *)(long)swfd;
-	dt_sdt_enable(dtp, prp);
+	return dt_sdt_enable(dtp, prp);
 }
 
 static void detach(dtrace_hdl_t *dtp, const dt_probe_t *prp)
-- 
2.43.5