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Message-ID: <Z_mI5UDV9ku9-1bG@z2>
Date: Fri, 11 Apr 2025 14:25:57 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Chun-Tse Shao <ctshao@...gle.com>
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...hat.com,
acme@...nel.org, mark.rutland@....com,
alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
irogers@...gle.com, adrian.hunter@...el.com,
kan.liang@...ux.intel.com, nick.forrington@....com,
linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v1] perf lock: Add --duration-filter option
Hello,
On Thu, Apr 10, 2025 at 10:24:19PM -0700, Chun-Tse Shao wrote:
> This patch introduces the `--duration-filter` option, allows users to
> exclude lock contention samples with durations shorter than the
> specified filter value.
>
> Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> ---
> tools/perf/Documentation/perf-lock.txt | 3 +++
> tools/perf/builtin-lock.c | 3 +++
> tools/perf/util/bpf_lock_contention.c | 22 ++++++++++++++-----
> .../perf/util/bpf_skel/lock_contention.bpf.c | 7 ++++++
> tools/perf/util/lock-contention.h | 1 +
> 5 files changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/Documentation/perf-lock.txt b/tools/perf/Documentation/perf-lock.txt
> index 859dc11a7372..1f57f5fc59e0 100644
> --- a/tools/perf/Documentation/perf-lock.txt
> +++ b/tools/perf/Documentation/perf-lock.txt
> @@ -216,6 +216,9 @@ CONTENTION OPTIONS
> --cgroup-filter=<value>::
> Show lock contention only in the given cgroups (comma separated list).
>
> +--duration-filter=<value>::
> + Filter out lock contention samples which durations less than the specified
> + value (default: 0). The unit is nanoseconds (ns).
Please follow the style like indentation and put a blank line after
this. Also you need to mention that it only works with BPF. I guess
you can add non-BPF support as well.
I'm not sure if nsec is a good choice since users may be interested in
usec or msec level contentions more. Maybe we can add unit to the
argument or default to usec and use 'double' type.
>
> SEE ALSO
> --------
> diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
> index 05e7bc30488a..d7b454e712bf 100644
> --- a/tools/perf/builtin-lock.c
> +++ b/tools/perf/builtin-lock.c
> @@ -60,6 +60,7 @@ static int stack_skip = CONTENTION_STACK_SKIP;
> static int print_nr_entries = INT_MAX / 2;
> static const char *output_name = NULL;
> static FILE *lock_output;
> +static int duration_filter;
>
> static struct lock_filter filters;
>
> @@ -2004,6 +2005,7 @@ static int __cmd_contention(int argc, const char **argv)
> .save_callstack = needs_callstack(),
> .owner = show_lock_owner,
> .cgroups = RB_ROOT,
> + .duration_filter = duration_filter,
> };
>
> lockhash_table = calloc(LOCKHASH_SIZE, sizeof(*lockhash_table));
> @@ -2580,6 +2582,7 @@ int cmd_lock(int argc, const char **argv)
> OPT_BOOLEAN(0, "lock-cgroup", &show_lock_cgroups, "show lock stats by cgroup"),
> OPT_CALLBACK('G', "cgroup-filter", NULL, "CGROUPS",
> "Filter specific cgroups", parse_cgroup_filter),
> + OPT_INTEGER(0, "duration-filter", &duration_filter, "Filter samples by duration"),
> OPT_PARENT(lock_options)
> };
>
> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index 5af8f6d1bc95..7b982a3e4000 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -203,6 +203,7 @@ int lock_contention_prepare(struct lock_contention *con)
> skel->rodata->aggr_mode = con->aggr_mode;
> skel->rodata->needs_callstack = con->save_callstack;
> skel->rodata->lock_owner = con->owner;
> + skel->rodata->duration_filter = con->duration_filter;
>
> if (con->aggr_mode == LOCK_AGGR_CGROUP || con->filters->nr_cgrps) {
> if (cgroup_is_v2("perf_event"))
> @@ -568,12 +569,23 @@ struct lock_stat *pop_owner_stack_trace(struct lock_contention *con)
> if (stack_trace == NULL)
> goto out_err;
>
> - if (bpf_map_get_next_key(stacks_fd, NULL, stack_trace))
> - goto out_err;
> + /*
> + * `owner_stacks` contains stacks recorded in `contention_begin()` that either never reached
> + * `contention_end()` or were filtered out and not stored in `owner_stat`. We skip if we
> + * cannot find corresponding `contention_data` in `owner_stat` with the given `stack_id`.
> + */
> + while (true) {
> + if (bpf_map_get_next_key(stacks_fd, NULL, stack_trace))
> + goto out_err;
> +
> + bpf_map_lookup_elem(stacks_fd, stack_trace, &stack_id);
> + ckey.stack_id = stack_id;
> + if (bpf_map_lookup_elem(stat_fd, &ckey, &cdata) == 0)
> + break;
>
> - bpf_map_lookup_elem(stacks_fd, stack_trace, &stack_id);
> - ckey.stack_id = stack_id;
> - bpf_map_lookup_elem(stat_fd, &ckey, &cdata);
> + /* Can not find `contention_data`, delete and skip. */
> + bpf_map_delete_elem(stacks_fd, stack_trace);
> + }
I think we can consider moving the callstack saving code to the
contention-end when the duration filter is used in order to reduce
overheads for to-be-filtered short contentions.
>
> st = zalloc(sizeof(struct lock_stat));
> if (!st)
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index 69be7a4234e0..26ddc0f21378 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -176,6 +176,7 @@ const volatile int stack_skip;
> const volatile int lock_owner;
> const volatile int use_cgroup_v2;
> const volatile int max_stack;
> +const volatile int duration_filter;
I think it should be u64 to save potentionally large durations.
>
> /* determine the key of lock stat */
> const volatile int aggr_mode;
> @@ -457,6 +458,9 @@ static inline void update_contention_data(struct contention_data *data, u64 dura
>
> static inline void update_owner_stat(u32 id, u64 duration, u32 flags)
> {
> + if (duration < duration_filter)
What if the duration_filter is 0? I'm not sure if BPF verifier can
optimize out the whole conditional block if it's 0.
Thanks,
Namhyung
> + return;
> +
> struct contention_key key = {
> .stack_id = id,
> .pid = 0,
> @@ -707,6 +711,9 @@ int contention_end(u64 *ctx)
> }
> }
> skip_owner:
> + if (duration < duration_filter)
> + goto out;
> +
> switch (aggr_mode) {
> case LOCK_AGGR_CALLER:
> key.stack_id = pelem->stack_id;
> diff --git a/tools/perf/util/lock-contention.h b/tools/perf/util/lock-contention.h
> index b5d916aa49df..97042e6d8b10 100644
> --- a/tools/perf/util/lock-contention.h
> +++ b/tools/perf/util/lock-contention.h
> @@ -149,6 +149,7 @@ struct lock_contention {
> int owner;
> int nr_filtered;
> bool save_callstack;
> + int duration_filter;
> };
>
> struct option;
> --
> 2.49.0.604.gff1f9ca942-goog
>
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