From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 164921714DC for ; Wed, 11 Sep 2024 09:30:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726047049; cv=none; b=iILWRajyho0DxT4qCuzbxg7NchuJKWWl3R6KCqYcV3A+ltZhsJa05LxcodWwE8vjn3LyHGpwABC1+/d0vxpoDqMOXUdPrBln+Ex6w/bg+SRUMHb5ob1llodkO2tDJtYYCRYq1MlciyQp+1P2XFUiKccbdwXh+pcZnmTEIsDXjwM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726047049; c=relaxed/simple; bh=Q44mqaTM1SIsrs8CgYvP0+W3Utf1yJBCLC/NqYnwdgQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=jQdCJxXngtgrkcfqYQedVv34fOAuLSI0v54m3G0OsD9G5J2/pECFYcHX18cD2e97INo44AUltywcuuRlaT7kLxqre4yqFR7WND1Dq3tqKdtKXKi1U2uALuS4rKKNY4VyodoTchlpohsRKi37LeZE7lGag6/j3jJj5T1/5YDcMIU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=rOUdYF5a; arc=none smtp.client-ip=209.85.128.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="rOUdYF5a" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-6d470831e3aso211858547b3.3 for ; Wed, 11 Sep 2024 02:30:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1726047047; x=1726651847; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=HIfiuZeJznqfh2tkLISY1veWrBubnfMuInZigqeP7X0=; b=rOUdYF5aHzX3C5dOczhvLlfXNDqHTk7L5abnBnXWeSVdTKMBXhwVx0q+bI/fHsTxJf BTILFv2FJaLlu8N8eAy4AioV66N/U0Gi4cEBeJ1JGJP/doekz4yuYpAYRzT22B5VH64G yh0iJe5fdPh2+2MeRU4dqK3y3FffFWFgFqdKTZdLigK8re7EkEax65Im0lrVL6L1g1Jn cjDdTl2cduuOIivR50mWMaKBIpNNtD6dbxYPYseYjUsqJfBKHs8XjDpkswntSn/+vD+S q9Cwo+trYMkQYeNKqHRb0XbtiGceTWtPZvF6vJrEd1YPcV+KcJ8QRjAZpgc8r3FchNcl JvKA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1726047047; x=1726651847; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=HIfiuZeJznqfh2tkLISY1veWrBubnfMuInZigqeP7X0=; b=FaYulCBlkZfELUQnd6y3B7fhBoLidwjbyCcp1t1mPfIXF3t+GBb58ChB02vD5zJcFW VYWd0Ugy819y8VRoeoLdatEciaxa2t7XxFP1G8LneemrAnzWeY36Cu25J7GxkBgBT+/n G/zswMIWP+L5sN/2fxqHMK00aRk+OwjrPJmd9TOzuso7F8/OmNLhkZzVEe9MXtvtuN1g hWKkj9OmXLeX0CTEUTgXoW/NkP7SubLYwdtVur7TUL83sIO/LQ2qOehpxScJmW9U996X xLncdjgLeby83+k1LpsehWkoEKpFvcgTqVBCqo1a67ROmwHVYyh9m/OO5bwR+SbgnKmN +a3A== X-Gm-Message-State: AOJu0YwFpVbc5Q5HPg1dNLeUlILcC4Jab+UM8WPP1tR+orlLlA1dlHS+ a8ofxsyWraffSiKLnAKbN++dFC4pEndbyt8E4AFNA/I0SGdv7dTQveRtVxAEA2QOlL0SlYzIgQT FxSBreem90Q5p2Nmr/A== X-Google-Smtp-Source: AGHT+IEtNHaw/88xokAWy+UiHnAdlVPy8NQA0O3wwzz1MkIfIbeu6r+aMsbXBRs/4d+Trw4L1hAPe+ThqsYRmZCe X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a25:9390:0:b0:e16:69e2:2028 with SMTP id 3f1490d57ef6-e1d34879f14mr32927276.3.1726047047060; Wed, 11 Sep 2024 02:30:47 -0700 (PDT) Date: Wed, 11 Sep 2024 10:30:17 +0100 In-Reply-To: <20240911093029.3279154-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240911093029.3279154-1-vdonnefort@google.com> X-Mailer: git-send-email 2.46.0.598.g6f2099f65c-goog Message-ID: <20240911093029.3279154-2-vdonnefort@google.com> Subject: [PATCH 01/13] ring-buffer: Check for empty ring-buffer with rb_num_of_entries() From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org, maz@kernel.org, oliver.upton@linux.dev Cc: kvmarm@lists.linux.dev, will@kernel.org, qperret@google.com, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" Currently there are two ways of identifying an empty ring-buffer. One relying on the current status of the commit / reader page (rb_per_cpu_empty()) and the other on the write and read counters (rb_num_of_entries() used in rb_get_reader_page()). with rb_num_of_entries(). This intends to ease later introduction of ring-buffer writers which are out of the kernel control and with whom, the only information available is through the meta-page counters. Signed-off-by: Vincent Donnefort diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index cebd879a30cb..7abe671effbf 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -3941,40 +3941,22 @@ int ring_buffer_write(struct trace_buffer *buffer, } EXPORT_SYMBOL_GPL(ring_buffer_write); -static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer) +/* + * The total entries in the ring buffer is the running counter + * of entries entered into the ring buffer, minus the sum of + * the entries read from the ring buffer and the number of + * entries that were overwritten. + */ +static inline unsigned long +rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer) { - struct buffer_page *reader = cpu_buffer->reader_page; - struct buffer_page *head = rb_set_head_page(cpu_buffer); - struct buffer_page *commit = cpu_buffer->commit_page; - - /* In case of error, head will be NULL */ - if (unlikely(!head)) - return true; - - /* Reader should exhaust content in reader page */ - if (reader->read != rb_page_size(reader)) - return false; - - /* - * If writers are committing on the reader page, knowing all - * committed content has been read, the ring buffer is empty. - */ - if (commit == reader) - return true; - - /* - * If writers are committing on a page other than reader page - * and head page, there should always be content to read. - */ - if (commit != head) - return false; + return local_read(&cpu_buffer->entries) - + (local_read(&cpu_buffer->overrun) + cpu_buffer->read); +} - /* - * Writers are committing on the head page, we just need - * to care about there're committed data, and the reader will - * swap reader page with head page when it is to read data. - */ - return rb_page_commit(commit) == 0; +static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer) +{ + return !rb_num_of_entries(cpu_buffer); } /** @@ -4120,19 +4102,6 @@ void ring_buffer_record_enable_cpu(struct trace_buffer *buffer, int cpu) } EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu); -/* - * The total entries in the ring buffer is the running counter - * of entries entered into the ring buffer, minus the sum of - * the entries read from the ring buffer and the number of - * entries that were overwritten. - */ -static inline unsigned long -rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer) -{ - return local_read(&cpu_buffer->entries) - - (local_read(&cpu_buffer->overrun) + cpu_buffer->read); -} - /** * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer * @buffer: The ring buffer -- 2.46.0.598.g6f2099f65c-goog