bpftune: tweak sampling to ensure at least one sample is collected

alan-maguire · alan-maguire · commit f2cd726949c7 · 2025-03-22T14:59:32.000Z
start sample count at 0 to ensure initial sample is taken; this
prevents us missing events of interest that are infrequent.

Signed-off-by: Alan Maguire &lt;alan.maguire@oracle.com&gt;
diff --git a/include/bpftune/bpftune.bpf.h b/include/bpftune/bpftune.bpf.h
@@ -305,7 +305,7 @@ do {								\
 								\
 	if (!sample.rate)					\
 		sample.rate = bpftune_sample_rate;		\
-	if (((++sample.count) % sample.rate) != 0)		\
+	if (((sample.count++) % sample.rate) != 0)		\
 		return 0;					\
 	last_ts = sample.ts;					\
 	sample.ts = bpf_ktime_get_ns();				\

Original file line number	Diff line number	Diff line change
`@@ -305,7 +305,7 @@ do { \`
`305`	`305`	`\`
`306`	`306`	`if (!sample.rate) \`
`307`	`307`	`sample.rate = bpftune_sample_rate; \`
`308`		`- if (((++sample.count) % sample.rate) != 0) \`
	`308`	`+ if (((sample.count++) % sample.rate) != 0) \`
`309`	`309`	`return 0; \`
`310`	`310`	`last_ts = sample.ts; \`
`311`	`311`	`sample.ts = bpf_ktime_get_ns(); \`