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Tue, 08 Sep 2026 07:27:34 -0700 (PDT) From: Mykyta Yatsenko Date: Tue, 08 Sep 2026 07:27:10 -0700 Subject: [PATCH bpf-next v3 1/3] bpftool: Track perf counter snapshot state Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260908-bpftool_cyles_per_run-v3-1-60e86f325c35@meta.com> References: <20260908-bpftool_cyles_per_run-v3-0-60e86f325c35@meta.com> In-Reply-To: <20260908-bpftool_cyles_per_run-v3-0-60e86f325c35@meta.com> To: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kernel-team@meta.com, eddyz87@gmail.com, memxor@gmail.com, qmo@kernel.org, linux-perf-users@vger.kernel.org, acme@kernel.org, namhyung@kernel.org Cc: Mykyta Yatsenko X-Mailer: b4 0.16-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1788877648; l=3143; i=yatsenko@meta.com; s=20260324; h=from:subject:message-id; bh=88iWtKcXxUazkWlhxqTHkjP1b2Zga7aQtAYNkuVTgac=; b=fmWe15Xe85smC0snYH9s6kKWbpvnTg5AiUs4LoaOm53baFwZsFceC/ccm/N+R/u9zad6i7h2d 6JvayRVkZFYCJTtdQcmJmic7UPkB1FmbN9hAYEof8MjnA4aAn1D5zxk X-Developer-Key: i=yatsenko@meta.com; a=ed25519; pk=1zCUBXUa66KmzfjNsG8YNlMj2ckPdqBPvFq2ww3/YaA= From: Mykyta Yatsenko A perf counter can be zero at fentry. PMU multiplexing can schedule the event during the BPF program. The old counter check then drops a valid sample. Use an armed flag to track each successful fentry snapshot. Reset all flags before new reads. The fexit path clears each flag when it consumes the snapshot. Fixes: 47c09d6a9f67 ("bpftool: Introduce "prog profile" command") Signed-off-by: Mykyta Yatsenko --- tools/bpf/bpftool/skeleton/profiler.bpf.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/tools/bpf/bpftool/skeleton/profiler.bpf.c b/tools/bpf/bpftool/skeleton/profiler.bpf.c index f48c783cb9f7..6c654bd9b346 100644 --- a/tools/bpf/bpftool/skeleton/profiler.bpf.c +++ b/tools/bpf/bpftool/skeleton/profiler.bpf.c @@ -10,6 +10,11 @@ struct bpf_perf_event_value___local { __u64 running; } __attribute__((preserve_access_index)); +struct profile_reading { + struct bpf_perf_event_value___local value; + bool armed; +}; + /* map of perf event fds, num_cpu * num_metric entries */ struct { __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY); @@ -21,7 +26,7 @@ struct { struct { __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY); __uint(key_size, sizeof(u32)); - __uint(value_size, sizeof(struct bpf_perf_event_value___local)); + __uint(value_size, sizeof(struct profile_reading)); } fentry_readings SEC(".maps"); /* accumulated readings */ @@ -45,7 +50,7 @@ const volatile __u32 num_metric = 1; SEC("fentry/XXX") int BPF_PROG(fentry_XXX) { - struct bpf_perf_event_value___local *ptrs[MAX_NUM_METRICS]; + struct profile_reading *ptrs[MAX_NUM_METRICS]; u32 key = bpf_get_smp_processor_id(); u32 i; @@ -56,6 +61,7 @@ int BPF_PROG(fentry_XXX) ptrs[i] = bpf_map_lookup_elem(&fentry_readings, &flag); if (!ptrs[i]) return 0; + ptrs[i]->armed = false; } for (i = 0; i < num_metric && i < MAX_NUM_METRICS; i++) { @@ -66,7 +72,8 @@ int BPF_PROG(fentry_XXX) sizeof(reading)); if (err) return 0; - *(ptrs[i]) = reading; + ptrs[i]->value = reading; + ptrs[i]->armed = true; key += num_cpu; } @@ -76,16 +83,18 @@ int BPF_PROG(fentry_XXX) static inline void fexit_update_maps(u32 id, struct bpf_perf_event_value___local *after) { - struct bpf_perf_event_value___local *before, diff; + struct profile_reading *before; + struct bpf_perf_event_value___local diff; before = bpf_map_lookup_elem(&fentry_readings, &id); /* only account samples with a valid fentry_reading */ - if (before && before->counter) { + if (before && before->armed) { struct bpf_perf_event_value___local *accum; - diff.counter = after->counter - before->counter; - diff.enabled = after->enabled - before->enabled; - diff.running = after->running - before->running; + before->armed = false; + diff.counter = after->counter - before->value.counter; + diff.enabled = after->enabled - before->value.enabled; + diff.running = after->running - before->value.running; accum = bpf_map_lookup_elem(&accum_readings, &id); if (accum) { -- 2.53.0-Meta