From nobody Mon Feb 9 15:06:43 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 490FA3BBD9; Mon, 15 Apr 2024 08:15:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713168902; cv=none; b=aZTfyzdUpkYcp38m542j8bAy2Ocq6hRbS9Eslo9tAgTa9YQzUndromo1VXQP9OU3hHSlgFHU7lQN43xI3qvi4XwA7JJOfzamKVPRlim8kc3SL3bEAc1idMji6yKUueSiZ+3w17i595g4hqhziwEbBWcog9HBAwPYqfuBoWcP1aA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713168902; c=relaxed/simple; bh=1vW++xN8zF1A0z3Y8yp49FhFAPI2if6N2fDvYtR7R4w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KmRAFrl5JjAYs7qR0jLJ6U/lMK5HqvrOUUb8LDUehiE+9CnlHBLuImzsIcadsH23Ir3AXgZ8Lskb/+PQr/ptGz0gjm41pBC3JGoWROwsUDhCknloT6a3b9z+DPY4fBaQEnPDa+OM8e5dfpIIKmtMXZd3uLvGFkMs/hde0rGrvqc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 170D81476; Mon, 15 Apr 2024 01:15:28 -0700 (PDT) Received: from e126817.cambridge.arm.com (e126817.cambridge.arm.com [10.2.3.5]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 14AAF3F64C; Mon, 15 Apr 2024 01:14:57 -0700 (PDT) From: Ben Gainey To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org Cc: james.clark@arm.com, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gainey Subject: [PATCH v5 1/4] perf: Support PERF_SAMPLE_READ with inherit Date: Mon, 15 Apr 2024 09:14:45 +0100 Message-ID: <20240415081448.123789-2-ben.gainey@arm.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240415081448.123789-1-ben.gainey@arm.com> References: <20240415081448.123789-1-ben.gainey@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This change allows events to use PERF_SAMPLE READ with inherit so long as PERF_SAMPLE_TID is also set. In this configuration, an event will be inherited into any child processes / threads, allowing convenient profiling of a multiprocess or multithreaded application, whilst allowing profiling tools to collect per-thread samples, in particular of groups of counters. The read_format field of both PERF_RECORD_READ and PERF_RECORD_SAMPLE are changed by this new configuration, but calls to `read()` on the same event file descriptor are unaffected and continue to return the cumulative total. Signed-off-by: Ben Gainey --- include/linux/perf_event.h | 1 + kernel/events/core.c | 82 ++++++++++++++++++++++++++++---------- 2 files changed, 62 insertions(+), 21 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index d2a15c0c6f8a..e7eed33c50f1 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -932,6 +932,7 @@ struct perf_event_context { =20 int nr_task_data; int nr_stat; + int nr_inherit_read; int nr_freq; int rotate_disable; =20 diff --git a/kernel/events/core.c b/kernel/events/core.c index 724e6d7e128f..bf0639a2e2b1 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1767,6 +1767,18 @@ perf_event_groups_next(struct perf_event *event, str= uct pmu *pmu) event =3D rb_entry_safe(rb_next(&event->group_node), \ typeof(*event), group_node)) =20 +/* + * Does the event attribute request inherit with PERF_SAMPLE_READ + */ +#define perf_attr_has_inherit_and_sample_read(attr) \ + ((attr)->inherit && ((attr)->sample_type & PERF_SAMPLE_READ)) + +/* + * Does the event request an attribte that requests inherit with PERF_SAMP= LE_READ + */ +#define perf_event_has_inherit_and_sample_read(event) \ + perf_attr_has_inherit_and_sample_read(&((event)->attr)) + /* * Add an event from the lists for its context. * Must be called with ctx->mutex and ctx->lock held. @@ -1797,6 +1809,8 @@ list_add_event(struct perf_event *event, struct perf_= event_context *ctx) ctx->nr_user++; if (event->attr.inherit_stat) ctx->nr_stat++; + if (perf_event_has_inherit_and_sample_read(event)) + ctx->nr_inherit_read++; =20 if (event->state > PERF_EVENT_STATE_OFF) perf_cgroup_event_enable(event, ctx); @@ -2021,6 +2035,8 @@ list_del_event(struct perf_event *event, struct perf_= event_context *ctx) ctx->nr_user--; if (event->attr.inherit_stat) ctx->nr_stat--; + if (perf_event_has_inherit_and_sample_read(event)) + ctx->nr_inherit_read--; =20 list_del_rcu(&event->event_entry); =20 @@ -3529,11 +3545,18 @@ perf_event_context_sched_out(struct task_struct *ta= sk, struct task_struct *next) perf_ctx_disable(ctx, false); =20 /* PMIs are disabled; ctx->nr_pending is stable. */ - if (local_read(&ctx->nr_pending) || + if (ctx->nr_inherit_read || + next_ctx->nr_inherit_read || + local_read(&ctx->nr_pending) || local_read(&next_ctx->nr_pending)) { /* * Must not swap out ctx when there's pending * events that rely on the ctx->task relation. + * + * Likewise, when a context contains inherit + + * SAMPLE_READ events they should be switched + * out using the slow path so that they are + * treated as if they were distinct contexts. */ raw_spin_unlock(&next_ctx->lock); rcu_read_unlock(); @@ -4533,11 +4556,19 @@ static void __perf_event_read(void *info) raw_spin_unlock(&ctx->lock); } =20 -static inline u64 perf_event_count(struct perf_event *event) +static inline u64 perf_event_count_cumulative(struct perf_event *event) { return local64_read(&event->count) + atomic64_read(&event->child_count); } =20 +static inline u64 perf_event_count(struct perf_event *event, bool self_val= ue_only) +{ + if (self_value_only && perf_event_has_inherit_and_sample_read(event)) + return local64_read(&event->count); + + return perf_event_count_cumulative(event); +} + static void calc_timer_values(struct perf_event *event, u64 *now, u64 *enabled, @@ -5454,7 +5485,7 @@ static u64 __perf_event_read_value(struct perf_event = *event, u64 *enabled, u64 * mutex_lock(&event->child_mutex); =20 (void)perf_event_read(event, false); - total +=3D perf_event_count(event); + total +=3D perf_event_count_cumulative(event); =20 *enabled +=3D event->total_time_enabled + atomic64_read(&event->child_total_time_enabled); @@ -5463,7 +5494,7 @@ static u64 __perf_event_read_value(struct perf_event = *event, u64 *enabled, u64 * =20 list_for_each_entry(child, &event->child_list, child_list) { (void)perf_event_read(child, false); - total +=3D perf_event_count(child); + total +=3D perf_event_count_cumulative(child); *enabled +=3D child->total_time_enabled; *running +=3D child->total_time_running; } @@ -5545,14 +5576,14 @@ static int __perf_read_group_add(struct perf_event = *leader, /* * Write {count,id} tuples for every sibling. */ - values[n++] +=3D perf_event_count(leader); + values[n++] +=3D perf_event_count_cumulative(leader); if (read_format & PERF_FORMAT_ID) values[n++] =3D primary_event_id(leader); if (read_format & PERF_FORMAT_LOST) values[n++] =3D atomic64_read(&leader->lost_samples); =20 for_each_sibling_event(sub, leader) { - values[n++] +=3D perf_event_count(sub); + values[n++] +=3D perf_event_count_cumulative(sub); if (read_format & PERF_FORMAT_ID) values[n++] =3D primary_event_id(sub); if (read_format & PERF_FORMAT_LOST) @@ -6132,7 +6163,7 @@ void perf_event_update_userpage(struct perf_event *ev= ent) ++userpg->lock; barrier(); userpg->index =3D perf_event_index(event); - userpg->offset =3D perf_event_count(event); + userpg->offset =3D perf_event_count_cumulative(event); if (userpg->index) userpg->offset -=3D local64_read(&event->hw.prev_count); =20 @@ -7194,13 +7225,14 @@ void perf_event__output_id_sample(struct perf_event= *event, =20 static void perf_output_read_one(struct perf_output_handle *handle, struct perf_event *event, - u64 enabled, u64 running) + u64 enabled, u64 running, + bool from_sample) { u64 read_format =3D event->attr.read_format; u64 values[5]; int n =3D 0; =20 - values[n++] =3D perf_event_count(event); + values[n++] =3D perf_event_count(event, from_sample); if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED) { values[n++] =3D enabled + atomic64_read(&event->child_total_time_enabled); @@ -7218,8 +7250,9 @@ static void perf_output_read_one(struct perf_output_h= andle *handle, } =20 static void perf_output_read_group(struct perf_output_handle *handle, - struct perf_event *event, - u64 enabled, u64 running) + struct perf_event *event, + u64 enabled, u64 running, + bool from_sample) { struct perf_event *leader =3D event->group_leader, *sub; u64 read_format =3D event->attr.read_format; @@ -7245,7 +7278,7 @@ static void perf_output_read_group(struct perf_output= _handle *handle, (leader->state =3D=3D PERF_EVENT_STATE_ACTIVE)) leader->pmu->read(leader); =20 - values[n++] =3D perf_event_count(leader); + values[n++] =3D perf_event_count(leader, from_sample); if (read_format & PERF_FORMAT_ID) values[n++] =3D primary_event_id(leader); if (read_format & PERF_FORMAT_LOST) @@ -7260,7 +7293,7 @@ static void perf_output_read_group(struct perf_output= _handle *handle, (sub->state =3D=3D PERF_EVENT_STATE_ACTIVE)) sub->pmu->read(sub); =20 - values[n++] =3D perf_event_count(sub); + values[n++] =3D perf_event_count(sub, from_sample); if (read_format & PERF_FORMAT_ID) values[n++] =3D primary_event_id(sub); if (read_format & PERF_FORMAT_LOST) @@ -7281,9 +7314,14 @@ static void perf_output_read_group(struct perf_outpu= t_handle *handle, * The problem is that its both hard and excessively expensive to iterate = the * child list, not to mention that its impossible to IPI the children runn= ing * on another CPU, from interrupt/NMI context. + * + * Instead the combination of PERF_SAMPLE_READ and inherit will track per-= thread + * counts rather than attempting to accumulate some value across all child= ren on + * all cores. */ static void perf_output_read(struct perf_output_handle *handle, - struct perf_event *event) + struct perf_event *event, + bool from_sample) { u64 enabled =3D 0, running =3D 0, now; u64 read_format =3D event->attr.read_format; @@ -7301,9 +7339,9 @@ static void perf_output_read(struct perf_output_handl= e *handle, calc_timer_values(event, &now, &enabled, &running); =20 if (event->attr.read_format & PERF_FORMAT_GROUP) - perf_output_read_group(handle, event, enabled, running); + perf_output_read_group(handle, event, enabled, running, from_sample); else - perf_output_read_one(handle, event, enabled, running); + perf_output_read_one(handle, event, enabled, running, from_sample); } =20 void perf_output_sample(struct perf_output_handle *handle, @@ -7343,7 +7381,7 @@ void perf_output_sample(struct perf_output_handle *ha= ndle, perf_output_put(handle, data->period); =20 if (sample_type & PERF_SAMPLE_READ) - perf_output_read(handle, event); + perf_output_read(handle, event, true); =20 if (sample_type & PERF_SAMPLE_CALLCHAIN) { int size =3D 1; @@ -7944,7 +7982,7 @@ perf_event_read_event(struct perf_event *event, return; =20 perf_output_put(&handle, read_event); - perf_output_read(&handle, event); + perf_output_read(&handle, event, false); perf_event__output_id_sample(event, &handle, &sample); =20 perf_output_end(&handle); @@ -12006,10 +12044,12 @@ perf_event_alloc(struct perf_event_attr *attr, in= t cpu, local64_set(&hwc->period_left, hwc->sample_period); =20 /* - * We currently do not support PERF_SAMPLE_READ on inherited events. + * We do not support PERF_SAMPLE_READ on inherited events unless + * PERF_SAMPLE_TID is also selected, which allows inherited events to + * collect per-thread samples. * See perf_output_read(). */ - if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ)) + if (perf_attr_has_inherit_and_sample_read(attr) && !(attr->sample_type & = PERF_SAMPLE_TID)) goto err_ns; =20 if (!has_branch_stack(event)) @@ -13033,7 +13073,7 @@ static void sync_child_event(struct perf_event *chi= ld_event) perf_event_read_event(child_event, task); } =20 - child_val =3D perf_event_count(child_event); + child_val =3D perf_event_count_cumulative(child_event); =20 /* * Add back the child's count to the parent's count: --=20 2.44.0