[tip:perf/urgent] perf core: Separate accounting of contexts and real addresses in a stack trace

From: tip-bot for Arnaldo Carvalho de Melo
Date: Fri May 20 2016 - 02:47:56 EST

Commit-ID: c85b03349640b34f3545503c8429fc43005e9a92
Gitweb: http://git.kernel.org/tip/c85b03349640b34f3545503c8429fc43005e9a92
Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Thu, 12 May 2016 13:06:21 -0300
Committer: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Mon, 16 May 2016 23:11:53 -0300

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 <adrian.hunter@xxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Milian Wolff <milian.wolff@xxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-3b4wnqk340c4sg4gwkfdi9yk@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
Documentation/sysctl/kernel.txt | 14 ++++++++++++++
include/linux/perf_event.h | 18 ++++++++++++++++--
include/uapi/linux/perf_event.h | 1 +
kernel/events/callchain.c | 10 +++++++++-
kernel/sysctl.c | 9 +++++++++
5 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index daabdd7..a3683ce 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -61,6 +61,7 @@ show up in /proc/sys/kernel:
- perf_cpu_time_max_percent
- perf_event_paranoid
- perf_event_max_stack
+- perf_event_max_contexts_per_stack
- pid_max
- powersave-nap [ PPC only ]
- printk
@@ -668,6 +669,19 @@ The default value is 127.

==============================================================

+perf_event_max_contexts_per_stack:
+
+Controls maximum number of stack frame context entries for
+(attr.sample_type & PERF_SAMPLE_CALLCHAIN) configured events, for
+instance, when using 'perf record -g' or 'perf trace --call-graph fp'.
+
+This can only be done when no events are in use that have callchains
+enabled, otherwise writing to this file will return -EBUSY.
+
+The default value is 8.
+
+==============================================================
+
pid_max:

PID allocation wrap value. When the kernel's next PID value
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2024b14..6b87be9 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;
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 43fc8d2..36ce552 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -862,6 +862,7 @@ enum perf_event_type {
};

#define PERF_MAX_STACK_DEPTH 127
+#define PERF_MAX_CONTEXTS_PER_STACK 8

enum perf_callchain_context {
PERF_CONTEXT_HV = (__u64)-32,
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index ca64573..179ef46 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -19,11 +19,13 @@ struct callchain_cpus_entries {
};

int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
+int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;

static inline size_t perf_callchain_entry__sizeof(void)
{
return (sizeof(struct perf_callchain_entry) +
- sizeof(__u64) * sysctl_perf_event_max_stack);
+ sizeof(__u64) * (sysctl_perf_event_max_stack +
+ sysctl_perf_event_max_contexts_per_stack));
}

static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
@@ -197,6 +199,8 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
ctx.entry = entry;
ctx.max_stack = max_stack;
ctx.nr = entry->nr = init_nr;
+ ctx.contexts = 0;
+ ctx.contexts_maxed = false;

if (kernel && !user_mode(regs)) {
if (add_mark)
@@ -228,6 +232,10 @@ exit_put:
return entry;
}

+/*
+ * Used for sysctl_perf_event_max_stack and
+ * sysctl_perf_event_max_contexts_per_stack.
+ */
int perf_event_max_stack_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 0ec6907..bec4c11 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1156,6 +1156,15 @@ static struct ctl_table kern_table[] = {
.extra1 = &zero,
.extra2 = &six_hundred_forty_kb,
},
+ {
+ .procname = "perf_event_max_contexts_per_stack",
+ .data = &sysctl_perf_event_max_contexts_per_stack,
+ .maxlen = sizeof(sysctl_perf_event_max_contexts_per_stack),
+ .mode = 0644,
+ .proc_handler = perf_event_max_stack_handler,
+ .extra1 = &zero,
+ .extra2 = &one_thousand,
+ },
#endif
#ifdef CONFIG_KMEMCHECK
{