From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1F46215D1 for ; Fri, 14 Mar 2025 00:02:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741910555; cv=none; b=YkpFvO0L/sRT/F86K6xGC6/475epO/KA0zcmpTwAKt00zY95KcqCtKOFbH5JnCbwVEk6SZfKHG94qgpkjttC1Wy9h/SyWf/mLs9LHwqo+DgpfDj8rGfA0nJbRu01SsgXrKmi7KN0TwPVGMZGj5D4ouH/LZFB3+g/ZEtHQE9Ha0E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741910555; c=relaxed/simple; bh=ddlU3uCWIy0JLBrSjZX2hg33GvWghng0Tcct8/x9G3A=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=C1OSg2hFQCZEHBpLcM9DTz4S0rhy4IMa8RCxAgjIknFwPNOsxjEqbHUGnnWdbjkFKLADa7n/mGuOwsBff0/lr96T30i6hI0w88+JHsR3Sc6QSD3/mc4Tz/N64qb1knU+qLSkQtfTcAJ2x1o85W9bLtRM2ZhpZUfc2zHJzwogx0A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=Ih+O1VUi; arc=none smtp.client-ip=198.175.65.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Ih+O1VUi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1741910555; x=1773446555; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=ddlU3uCWIy0JLBrSjZX2hg33GvWghng0Tcct8/x9G3A=; b=Ih+O1VUiOD133onVBVlz2pHapEnANLjFlsqZIu/RUUleiogNLUHLt8si blvTayLG3H/UrjUiLUVlVj9HpTa29Lzf1wAazEUGZgvA/RiL83JFT5WU1 fYRcZ0IS7iDtY7UgqQEn9R8pCbioRIa4rCPfH+cs02U+BuDDjw73j6aVT 4Bz8UI4iwNvI9DEfr6dScNxt7PexarAG1OSXkNGecuATG0crkTUeenoRf J95qg8PEsj20emy+Nozw3WQpq954oCmvb2TBFgkvlTlvREtt3tgtC5PIQ iy212Ek0ys/z5othjK2pRR9mY+zMzZq0W48sDGQmVDO0/G6qnhPLxSOfu g==; X-CSE-ConnectionGUID: BUAuspKhT1eQSoNF+BINag== X-CSE-MsgGUID: 3vu0bN18RZGtoLoReX0rLA== X-IronPort-AV: E=McAfee;i="6700,10204,11372"; a="43160662" X-IronPort-AV: E=Sophos;i="6.14,246,1736841600"; d="scan'208";a="43160662" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by orvoesa108.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Mar 2025 17:02:31 -0700 X-CSE-ConnectionGUID: BXq7sXyJSQqwVHR3gmWFjA== X-CSE-MsgGUID: 58dmASXoSOO+sv1wjzPAMA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.14,246,1736841600"; d="scan'208";a="125986545" Received: from kanliang-dev.jf.intel.com ([10.165.154.102]) by orviesa003.jf.intel.com with ESMTP; 13 Mar 2025 17:02:31 -0700 From: kan.liang@linux.intel.com To: peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de, bp@alien8.de, acme@kernel.org, namhyung@kernel.org, irogers@google.com, linux-kernel@vger.kernel.org Cc: ak@linux.intel.com, eranian@google.com, Kan Liang Subject: [PATCH V9 3/7] perf: attach/detach PMU specific data Date: Thu, 13 Mar 2025 17:02:38 -0700 Message-Id: <20250314000242.323199-3-kan.liang@linux.intel.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20250314000242.323199-1-kan.liang@linux.intel.com> References: <20250314000242.323199-1-kan.liang@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kan Liang The LBR call stack data has to be saved/restored during context switch to fix the shorter LBRs call stacks issue in the system-wide mode. Allocate PMU specific data and attach them to the corresponding task_struct during LBR call stack monitoring. When a LBR call stack event is accounted, the perf_ctx_data for the related tasks will be allocated/attached by attach_perf_ctx_data(). When a LBR call stack event is unaccounted, the perf_ctx_data for related tasks will be detached/freed by detach_perf_ctx_data(). The LBR call stack event could be a per-task event or a system-wide event. - For a per-task event, perf only allocates the perf_ctx_data for the current task. If the allocation fails, perf will error out. - For a system-wide event, perf has to allocate the perf_ctx_data for both the existing tasks and the upcoming tasks. The allocation for the existing tasks is done in perf_event_alloc(). If any allocation fails, perf will error out. The allocation for the new tasks will be done in perf_event_fork(). A global reader/writer semaphore, global_ctx_data_rwsem, is added to address the global race. - The perf_ctx_data only be freed by the last LBR call stack event. The number of the per-task events is tracked by refcount of each task. Since the system-wide events impact all tasks, it's not practical to go through the whole task list to update the refcount for each system-wide event. The number of system-wide events is tracked by a global variable global_ctx_data_ref. Suggested-by: Peter Zijlstra (Intel) Signed-off-by: Kan Liang --- Changes since V8 - Apply guard for rw semaphore and rcu lock kernel/events/core.c | 276 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 276 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index 2e5f0a204484..d2bef9dfe23b 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -55,6 +55,7 @@ #include #include #include +#include #include "internal.h" @@ -5212,6 +5213,217 @@ static void unaccount_freq_event(void) atomic_dec(&nr_freq_events); } + +static struct perf_ctx_data * +alloc_perf_ctx_data(struct kmem_cache *ctx_cache, bool global) +{ + struct perf_ctx_data *cd; + + cd = kzalloc(sizeof(*cd), GFP_KERNEL); + if (!cd) + return NULL; + + cd->data = kmem_cache_zalloc(ctx_cache, GFP_KERNEL); + if (!cd->data) { + kfree(cd); + return NULL; + } + + cd->global = global; + cd->ctx_cache = ctx_cache; + refcount_set(&cd->refcount, 1); + + return cd; +} + +static void free_perf_ctx_data(struct perf_ctx_data *cd) +{ + kmem_cache_free(cd->ctx_cache, cd->data); + kfree(cd); +} + +static void __free_perf_ctx_data_rcu(struct rcu_head *rcu_head) +{ + struct perf_ctx_data *cd; + + cd = container_of(rcu_head, struct perf_ctx_data, rcu_head); + free_perf_ctx_data(cd); +} + +static inline void perf_free_ctx_data_rcu(struct perf_ctx_data *cd) +{ + call_rcu(&cd->rcu_head, __free_perf_ctx_data_rcu); +} + +static int +attach_task_ctx_data(struct task_struct *task, struct kmem_cache *ctx_cache, + bool global) +{ + struct perf_ctx_data *cd, *old = NULL; + + cd = alloc_perf_ctx_data(ctx_cache, global); + if (!cd) + return -ENOMEM; + + for (;;) { + if (try_cmpxchg((struct perf_ctx_data **)&task->perf_ctx_data, &old, cd)) { + if (old) + perf_free_ctx_data_rcu(old); + return 0; + } + + if (!old) { + /* + * After seeing a dead @old, we raced with + * removal and lost, try again to install @cd. + */ + continue; + } + + if (refcount_inc_not_zero(&old->refcount)) { + free_perf_ctx_data(cd); /* unused */ + return 0; + } + + /* + * @old is a dead object, refcount==0 is stable, try and + * replace it with @cd. + */ + } + return 0; +} + +static void __detach_global_ctx_data(void); +DEFINE_STATIC_PERCPU_RWSEM(global_ctx_data_rwsem); +static refcount_t global_ctx_data_ref; + +static int +attach_global_ctx_data(struct kmem_cache *ctx_cache) +{ + struct task_struct *g, *p; + struct perf_ctx_data *cd; + int ret; + + if (refcount_inc_not_zero(&global_ctx_data_ref)) + return 0; + + guard(percpu_write)(&global_ctx_data_rwsem); + if (refcount_inc_not_zero(&global_ctx_data_ref)) + return 0; +again: + /* Allocate everything */ + scoped_guard (rcu) { + for_each_process_thread(g, p) { + cd = rcu_dereference(p->perf_ctx_data); + if (cd && !cd->global) { + cd->global = 1; + if (!refcount_inc_not_zero(&cd->refcount)) + cd = NULL; + } + if (!cd) { + get_task_struct(p); + goto alloc; + } + } + } + + refcount_set(&global_ctx_data_ref, 1); + + return 0; +alloc: + ret = attach_task_ctx_data(p, ctx_cache, true); + put_task_struct(p); + if (ret) { + __detach_global_ctx_data(); + return ret; + } + goto again; +} + +static int +attach_perf_ctx_data(struct perf_event *event) +{ + struct task_struct *task = event->hw.target; + struct kmem_cache *ctx_cache = event->pmu->task_ctx_cache; + + if (!ctx_cache) + return -ENOMEM; + + if (task) + return attach_task_ctx_data(task, ctx_cache, false); + else + return attach_global_ctx_data(ctx_cache); +} + +static void +detach_task_ctx_data(struct task_struct *p) +{ + struct perf_ctx_data *cd; + + scoped_guard (rcu) { + cd = rcu_dereference(p->perf_ctx_data); + if (!cd || !refcount_dec_and_test(&cd->refcount)) + return; + } + + /* + * The old ctx_data may be lost because of the race. + * Nothing is required to do for the case. + * See attach_task_ctx_data(). + */ + if (try_cmpxchg((struct perf_ctx_data **)&p->perf_ctx_data, &cd, NULL)) + perf_free_ctx_data_rcu(cd); +} + +static void __detach_global_ctx_data(void) +{ + struct task_struct *g, *p; + struct perf_ctx_data *cd; + +again: + scoped_guard (rcu) { + for_each_process_thread(g, p) { + cd = rcu_dereference(p->perf_ctx_data); + if (!cd || !cd->global) + continue; + cd->global = 0; + get_task_struct(p); + goto detach; + } + } + return; +detach: + detach_task_ctx_data(p); + put_task_struct(p); + goto again; +} + +static void detach_global_ctx_data(void) +{ + if (refcount_dec_not_one(&global_ctx_data_ref)) + return; + + guard(percpu_write)(&global_ctx_data_rwsem); + if (!refcount_dec_and_test(&global_ctx_data_ref)) + return; + + /* remove everything */ + __detach_global_ctx_data(); +} + +static void detach_perf_ctx_data(struct perf_event *event) +{ + struct task_struct *task = event->hw.target; + + if (!event->pmu->task_ctx_cache) + return; + + if (task) + detach_task_ctx_data(task); + else + detach_global_ctx_data(); +} + static void unaccount_event(struct perf_event *event) { bool dec = false; @@ -5249,6 +5461,8 @@ static void unaccount_event(struct perf_event *event) atomic_dec(&nr_bpf_events); if (event->attr.text_poke) atomic_dec(&nr_text_poke_events); + if (event->attach_state & PERF_ATTACH_TASK_DATA) + detach_perf_ctx_data(event); if (dec) { if (!atomic_add_unless(&perf_sched_count, -1, 1)) @@ -8598,10 +8812,58 @@ static void perf_event_task(struct task_struct *task, task_ctx); } +/* + * Allocate data for a new task when profiling system-wide + * events which require PMU specific data + */ +static void +perf_event_alloc_task_data(struct task_struct *child, + struct task_struct *parent) +{ + struct kmem_cache *ctx_cache = NULL; + struct perf_ctx_data *cd; + + if (!refcount_read(&global_ctx_data_ref)) + return; + + scoped_guard (rcu) { + cd = rcu_dereference(parent->perf_ctx_data); + if (cd) + ctx_cache = cd->ctx_cache; + } + + if (!ctx_cache) + return; + + guard(percpu_read)(&global_ctx_data_rwsem); + scoped_guard (rcu) { + cd = rcu_dereference(child->perf_ctx_data); + if (!cd) { + /* + * A system-wide event may be unaccount, + * when attaching the perf_ctx_data. + */ + if (!refcount_read(&global_ctx_data_ref)) + return; + goto attach; + } + + if (!cd->global) { + cd->global = 1; + refcount_inc(&cd->refcount); + } + } + + return; +attach: + attach_task_ctx_data(child, ctx_cache, true); +} + void perf_event_fork(struct task_struct *task) { perf_event_task(task, NULL, 1); perf_event_namespaces(task); + perf_event_alloc_task_data(task, current); } /* @@ -12551,6 +12813,14 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, if (err) return ERR_PTR(err); + if (event->attach_state & PERF_ATTACH_TASK_DATA) { + err = attach_perf_ctx_data(event); + if (err) { + security_perf_event_free(event); + return ERR_PTR(err); + } + } + /* symmetric to unaccount_event() in _free_event() */ account_event(event); @@ -13628,6 +13898,12 @@ void perf_event_exit_task(struct task_struct *child) * At this point we need to send EXIT events to cpu contexts. */ perf_event_task(child, NULL, 0); + + /* + * Detach the perf_ctx_data for the system-wide event. + */ + guard(percpu_read)(&global_ctx_data_rwsem); + detach_task_ctx_data(child); } static void perf_free_event(struct perf_event *event, -- 2.38.1