Re: [PATCH v3 1/5] perf lock: Add bpf maps for owner stack tracing

[Namhyung Kim <namhyung@kernel.org>]

On Tue, Jan 28, 2025 at 04:14:57PM -0800, Chun-Tse Shao wrote:
> Add a struct and few bpf maps in order to tracing owner stack.
> `struct owner_tracing_data`: Contains owner's pid, stack id, timestamp for
>   when the owner acquires lock, and the count of lock waiters.
> `stack_buf`: Percpu buffer for retrieving owner stacktrace.
> `owner_stacks`: For tracing owner stacktrace to customized owner stack id.
> `owner_data`: For tracing lock_address to `struct owner_tracing_data` in
>   bpf program.
> `owner_stat`: For reporting owner stacktrace in usermode.
> 
> Signed-off-by: Chun-Tse Shao <ctshao@google.com>
> ---
>  tools/perf/util/bpf_lock_contention.c         | 16 +++++--
>  .../perf/util/bpf_skel/lock_contention.bpf.c  | 42 ++++++++++++++++---
>  tools/perf/util/bpf_skel/lock_data.h          |  7 ++++
>  3 files changed, 57 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index fc8666222399..795e2374facc 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -131,9 +131,19 @@ int lock_contention_prepare(struct lock_contention *con)
>  	else
>  		bpf_map__set_max_entries(skel->maps.task_data, 1);
>  
> -	if (con->save_callstack)
> -		bpf_map__set_max_entries(skel->maps.stacks, con->map_nr_entries);
> -	else
> +	if (con->save_callstack) {
> +		bpf_map__set_max_entries(skel->maps.stacks,
> +					 con->map_nr_entries);

It can be on the same line as it used to be.


> +		if (con->owner) {
> +			bpf_map__set_value_size(skel->maps.stack_buf, con->max_stack * sizeof(u64));
> +			bpf_map__set_key_size(skel->maps.owner_stacks,
> +						con->max_stack * sizeof(u64));
> +			bpf_map__set_max_entries(skel->maps.owner_stacks, con->map_nr_entries);
> +			bpf_map__set_max_entries(skel->maps.owner_data, con->map_nr_entries);
> +			bpf_map__set_max_entries(skel->maps.owner_stat, con->map_nr_entries);
> +			skel->rodata->max_stack = con->max_stack;
> +		}
> +	} else

Please add parenthesis even for single line when the matching if block
has parenthesis.


>  		bpf_map__set_max_entries(skel->maps.stacks, 1);
>  
>  	if (target__has_cpu(target)) {
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index 6533ea9b044c..b4961dd86222 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -19,13 +19,37 @@
>  #define LCB_F_PERCPU	(1U << 4)
>  #define LCB_F_MUTEX	(1U << 5)
>  
> -/* callstack storage  */
> + /* buffer for owner stacktrace */
>  struct {
> -	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
> +	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
>  	__uint(key_size, sizeof(__u32));
>  	__uint(value_size, sizeof(__u64));
> -	__uint(max_entries, MAX_ENTRIES);
> -} stacks SEC(".maps");
> +	__uint(max_entries, 1);
> +} stack_buf SEC(".maps");
> +
> +/* a map for tracing owner stacktrace to owner stack id */
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(__u64)); // owner stacktrace
> +	__uint(value_size, sizeof(__u64)); // owner stack id
> +	__uint(max_entries, 1);
> +} owner_stacks SEC(".maps");
> +
> +/* a map for tracing lock address to owner data */
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(__u64)); // lock address
> +	__uint(value_size, sizeof(struct owner_tracing_data));
> +	__uint(max_entries, 1);
> +} owner_data SEC(".maps");
> +
> +/* a map for contention_key (stores owner stack id) to contention data */
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(struct contention_key));
> +	__uint(value_size, sizeof(struct contention_data));
> +	__uint(max_entries, 1);
> +} owner_stat SEC(".maps");
>  
>  /* maintain timestamp at the beginning of contention */
>  struct {
> @@ -43,6 +67,14 @@ struct {
>  	__uint(max_entries, 1);
>  } tstamp_cpu SEC(".maps");
>  
> +/* callstack storage  */
> +struct {
> +	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u64));
> +	__uint(max_entries, MAX_ENTRIES);
> +} stacks SEC(".maps");

Can you please keep this on top of the maps so that it can minimize the
diff?  I think it's better to move the new owner related stuff to
bottom.

> +
>  /* actual lock contention statistics */
>  struct {
>  	__uint(type, BPF_MAP_TYPE_HASH);
> @@ -143,6 +175,7 @@ const volatile int needs_callstack;
>  const volatile int stack_skip;
>  const volatile int lock_owner;
>  const volatile int use_cgroup_v2;
> +const volatile int max_stack;
>  
>  /* determine the key of lock stat */
>  const volatile int aggr_mode;
> @@ -466,7 +499,6 @@ int contention_end(u64 *ctx)
>  			return 0;
>  		need_delete = true;
>  	}
> -

Not needed.

Thanks,
Namhyung


>  	duration = bpf_ktime_get_ns() - pelem->timestamp;
>  	if ((__s64)duration < 0) {
>  		__sync_fetch_and_add(&time_fail, 1);
> diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
> index c15f734d7fc4..15f5743bd409 100644
> --- a/tools/perf/util/bpf_skel/lock_data.h
> +++ b/tools/perf/util/bpf_skel/lock_data.h
> @@ -3,6 +3,13 @@
>  #ifndef UTIL_BPF_SKEL_LOCK_DATA_H
>  #define UTIL_BPF_SKEL_LOCK_DATA_H
>  
> +struct owner_tracing_data {
> +	u32 pid; // Who has the lock.
> +	u32 count; // How many waiters for this lock.
> +	u64 timestamp; // The time while the owner acquires lock and contention is going on.
> +	s32 stack_id; // Identifier for `owner_stat`, which stores as value in `owner_stacks`
> +};
> +
>  struct tstamp_data {
>  	u64 timestamp;
>  	u64 lock;
> -- 
> 2.48.1.262.g85cc9f2d1e-goog
>