perf core: Separate accounting of contexts and real addresses in a stack trace

The perf_sample->ip_callchain->nr value includes all the entries in the
ip_callchain->ip[] array, real addresses and PERF_CONTEXT_{KERNEL,USER,etc},
while what the user expects is that what is in the kernel.perf_event_max_stack
sysctl or in the upcoming per event perf_event_attr.sample_max_stack knob be
honoured in terms of IP addresses in the stack trace.

So allocate a bunch of extra entries for contexts, and do the accounting
via perf_callchain_entry_ctx struct members.

A new sysctl, kernel.perf_event_max_contexts_per_stack is also
introduced for investigating possible bugs in the callchain
implementation by some arch.

Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Brendan Gregg <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Milian Wolff <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: Wang Nan <[email protected]>
Cc: Zefan Li <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files changed, 16 insertions, 2 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2024b14cc2b1..6b87be908790 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -65,6 +65,8 @@ struct perf_callchain_entry_ctx {
 	struct perf_callchain_entry *entry;
 	u32			    max_stack;
 	u32			    nr;
+	short			    contexts;
+	bool			    contexts_maxed;
 };
 
 struct perf_raw_record {
@@ -1078,12 +1080,24 @@ extern int get_callchain_buffers(void);
 extern void put_callchain_buffers(void);
 
 extern int sysctl_perf_event_max_stack;
+extern int sysctl_perf_event_max_contexts_per_stack;
 
-#define perf_callchain_store_context(ctx, context) perf_callchain_store(ctx, context)
+static inline int perf_callchain_store_context(struct perf_callchain_entry_ctx *ctx, u64 ip)
+{
+	if (ctx->contexts < sysctl_perf_event_max_contexts_per_stack) {
+		struct perf_callchain_entry *entry = ctx->entry;
+		entry->ip[entry->nr++] = ip;
+		++ctx->contexts;
+		return 0;
+	} else {
+		ctx->contexts_maxed = true;
+		return -1; /* no more room, stop walking the stack */
+	}
+}
 
 static inline int perf_callchain_store(struct perf_callchain_entry_ctx *ctx, u64 ip)
 {
-	if (ctx->nr < ctx->max_stack) {
+	if (ctx->nr < ctx->max_stack && !ctx->contexts_maxed) {
 		struct perf_callchain_entry *entry = ctx->entry;
 		entry->ip[entry->nr++] = ip;
 		++ctx->nr;