From patchwork Wed Jul 1 16:11:52 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Alex_Benn=C3=A9e?= X-Patchwork-Id: 11636819 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BE56B60D for ; Wed, 1 Jul 2020 16:15:47 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 959DB20760 for ; Wed, 1 Jul 2020 16:15:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="qT/4txte" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 959DB20760 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:51108 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jqfOk-0004Jz-MI for patchwork-qemu-devel@patchwork.kernel.org; Wed, 01 Jul 2020 12:15:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40108) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jqfL8-0007Ds-5m for qemu-devel@nongnu.org; Wed, 01 Jul 2020 12:12:02 -0400 Received: from mail-wr1-x443.google.com ([2a00:1450:4864:20::443]:45830) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jqfL4-0006GM-Fc for qemu-devel@nongnu.org; Wed, 01 Jul 2020 12:12:01 -0400 Received: by mail-wr1-x443.google.com with SMTP id s10so24588250wrw.12 for ; Wed, 01 Jul 2020 09:11:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=plqX1uLjHS1JRtUyTbOdw9sOOjMvjpQ/src1XYAUVDM=; b=qT/4txteqaajJk5C+0hMAnHFYeTIx/JBSqvSnfmpWrKhkPM+MCh0ieWDsBE3riGg5S pwaFghfibw4x5VvpkTeBLf9mq7lbr//vb1L6lKK/P05QmrqtyDHtalxFKHI6MMSjcsy3 of8Wecu4iGPV7kjHnrvB7tMOX7eFtSvwWFRVPVs/Mz+kWAk6lZl3aW9p3EfT6+ZKpLtQ W3KWGhl5dy+coKb12u7szq9y2A3Mf6eka05F/hmsRSH+md4i/wCSLYJQY4thgCT7lhZS aGpNfZOjYgL4MnIReIqfuVEa6MrldM42YV5rTo60Vcpn+tYl3MteisEICZt7KyQ1Vpyi fjkQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=plqX1uLjHS1JRtUyTbOdw9sOOjMvjpQ/src1XYAUVDM=; b=LGL7oZerFZhLbGt0oARIYOle/J4gYP9ej7EG/Fd+xHfq50z8jVhQ2Oqv8o6NH0M7Uh ReABiCRnzud/K7FCTBSdSYizVFjJVCRFaxhMbU/RRAgoIXMtfF3oRUpRFN7wYRN7Ezmk gZD3vNqnNI9tGfu34JcxlLCGcHZ5TmEnFDr6wl3p7DbtUn4Zv+d/gF62SHy+25cbHhnK qjiGeT2EuAczZaHa8dHwNTVUySLgesiX4e7leYMsZqqr3VXlsucy34OTftWAf2z2ypuV lpURVOL/6BLzEKszCB4isKthYyDoFdYDM5FA4o0Fndjz+Gzoz87QFpq4+ZlpgulNj2Va KqNg== X-Gm-Message-State: AOAM533U9qI1FBu4DNH1c9s5XCiz9rlndc/zZ0wE3ZR3H3hPq9Cs8EOx VlpaAr5oZRpkiU+I2u2s3S221Q== X-Google-Smtp-Source: ABdhPJxhbFM3ysjxh1hMwdGkW6s+aPuVHA0F88oKfI/tGJhhz3nBanOa/ZWjT9l1ZQ54APNIw+L7aQ== X-Received: by 2002:adf:f60c:: with SMTP id t12mr29586194wrp.198.1593619916565; Wed, 01 Jul 2020 09:11:56 -0700 (PDT) Received: from zen.linaroharston ([51.148.130.216]) by smtp.gmail.com with ESMTPSA id z17sm8248687wmc.3.2020.07.01.09.11.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2020 09:11:54 -0700 (PDT) Received: from zen.lan (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id 7EA2E1FF8C; Wed, 1 Jul 2020 17:11:53 +0100 (BST) From: =?utf-8?q?Alex_Benn=C3=A9e?= To: qemu-devel@nongnu.org Subject: [PATCH v2 2/3] docs/devel: convert and update MTTCG design document Date: Wed, 1 Jul 2020 17:11:52 +0100 Message-Id: <20200701161153.30988-3-alex.bennee@linaro.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200701161153.30988-1-alex.bennee@linaro.org> References: <20200701161153.30988-1-alex.bennee@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::443; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x443.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?utf-8?q?Alex_Benn=C3=A9e?= Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" Do a light conversion to .rst and clean-up some of the language at the start now MTTCG has been merged for a while. Signed-off-by: Alex Bennée Reviewed-by: Richard Henderson --- docs/devel/index.rst | 1 + ...ti-thread-tcg.txt => multi-thread-tcg.rst} | 52 ++++++++++++------- 2 files changed, 34 insertions(+), 19 deletions(-) rename docs/devel/{multi-thread-tcg.txt => multi-thread-tcg.rst} (90%) diff --git a/docs/devel/index.rst b/docs/devel/index.rst index bb8238c5d6d..4ecaea3643f 100644 --- a/docs/devel/index.rst +++ b/docs/devel/index.rst @@ -23,6 +23,7 @@ Contents: decodetree secure-coding-practices tcg + multi-thread-tcg tcg-plugins bitops reset diff --git a/docs/devel/multi-thread-tcg.txt b/docs/devel/multi-thread-tcg.rst similarity index 90% rename from docs/devel/multi-thread-tcg.txt rename to docs/devel/multi-thread-tcg.rst index 3c85ac0eab9..42158b77c70 100644 --- a/docs/devel/multi-thread-tcg.txt +++ b/docs/devel/multi-thread-tcg.rst @@ -1,15 +1,17 @@ -Copyright (c) 2015-2016 Linaro Ltd. +.. + Copyright (c) 2015-2020 Linaro Ltd. -This work is licensed under the terms of the GNU GPL, version 2 or -later. See the COPYING file in the top-level directory. + This work is licensed under the terms of the GNU GPL, version 2 or + later. See the COPYING file in the top-level directory. Introduction ============ -This document outlines the design for multi-threaded TCG system-mode -emulation. The current user-mode emulation mirrors the thread -structure of the translated executable. Some of the work will be -applicable to both system and linux-user emulation. +This document outlines the design for multi-threaded TCG (a.k.a MTTCG) +system-mode emulation. user-mode emulation has always mirrored the +thread structure of the translated executable although some of the +changes done for MTTCG system emulation have improved the stability of +linux-user emulation. The original system-mode TCG implementation was single threaded and dealt with multiple CPUs with simple round-robin scheduling. This @@ -21,9 +23,18 @@ vCPU Scheduling =============== We introduce a new running mode where each vCPU will run on its own -user-space thread. This will be enabled by default for all FE/BE -combinations that have had the required work done to support this -safely. +user-space thread. This is enabled by default for all FE/BE +combinations where the host memory model is able to accommodate the +guest (TCG_GUEST_DEFAULT_MO & ~TCG_TARGET_DEFAULT_MO is zero) and the +guest has had the required work done to support this safely +(TARGET_SUPPORTS_MTTCG). + +System emulation will fall back to the original round robin approach +if: + +* forced by --accel tcg,thread=single +* enabling --icount mode +* 64 bit guests on 32 bit hosts (TCG_OVERSIZED_GUEST) In the general case of running translated code there should be no inter-vCPU dependencies and all vCPUs should be able to run at full @@ -61,7 +72,9 @@ have their block-to-block jumps patched. Global TCG State ---------------- -### User-mode emulation +User-mode emulation +~~~~~~~~~~~~~~~~~~~ + We need to protect the entire code generation cycle including any post generation patching of the translated code. This also implies a shared translation buffer which contains code running on all cores. Any @@ -78,9 +91,11 @@ patching. Code generation is serialised with mmap_lock(). -### !User-mode emulation +!User-mode emulation +~~~~~~~~~~~~~~~~~~~~ + Each vCPU has its own TCG context and associated TCG region, thereby -requiring no locking. +requiring no locking during translation. Translation Blocks ------------------ @@ -92,6 +107,7 @@ including: - debugging operations (breakpoint insertion/removal) - some CPU helper functions + - linux-user spawning it's first thread This is done with the async_safe_run_on_cpu() mechanism to ensure all vCPUs are quiescent when changes are being made to shared global @@ -250,8 +266,10 @@ to enforce a particular ordering of memory operations from the point of view of external observers (e.g. another processor core). They can apply to any memory operations as well as just loads or stores. -The Linux kernel has an excellent write-up on the various forms of -memory barrier and the guarantees they can provide [1]. +The Linux kernel has an excellent `write-up +` +on the various forms of memory barrier and the guarantees they can +provide. Barriers are often wrapped around synchronisation primitives to provide explicit memory ordering semantics. However they can be used @@ -352,7 +370,3 @@ an exclusive lock which ensures all emulation is serialised. While the atomic helpers look good enough for now there may be a need to look at solutions that can more closely model the guest architectures semantics. - -========== - -[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/memory-barriers.txt