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Fri, 25 Jul 2025 08:45:26 -0700 (PDT) From: =?UTF-8?q?Alex=20Benn=C3=A9e?= To: qemu-devel@nongnu.org Cc: Thomas Huth , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Paolo Bonzini , =?UTF-8?q?Alex=20Benn=C3=A9e?= , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= Subject: [PATCH for 10.1 v2 05/14] docs/user: expand section on threading Date: Fri, 25 Jul 2025 16:45:08 +0100 Message-ID: <20250725154517.3523095-6-alex.bennee@linaro.org> X-Mailer: git-send-email 2.47.2 In-Reply-To: <20250725154517.3523095-1-alex.bennee@linaro.org> References: <20250725154517.3523095-1-alex.bennee@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::631; envelope-from=alex.bennee@linaro.org; helo=mail-ej1-x631.google.com 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=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @linaro.org) X-ZM-MESSAGEID: 1753458638012116600 Potentially too many weasel words when describing atomic and memory order issues. Signed-off-by: Alex Benn=C3=A9e Reviewed-by: Richard Henderson --- v2 - /we are limit/we limit/ - use QEMU -user-mode process instead of guest --- docs/user/main.rst | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/docs/user/main.rst b/docs/user/main.rst index 05de904225c..347bdfabf8c 100644 --- a/docs/user/main.rst +++ b/docs/user/main.rst @@ -46,9 +46,15 @@ Threading =20 On Linux, QEMU can emulate the ``clone`` syscall and create a real host thread (with a separate virtual CPU) for each emulated thread. -Note that not all targets currently emulate atomic operations -correctly. x86 and Arm use a global lock in order to preserve their -semantics. +However as QEMU relies on the system libc to call ``clone`` on its +behalf we limit the flags accepted to those it uses. Specifically this +means flags affecting namespaces (e.g. container runtimes) are not +supported. QEMU user-mode processes can still be run inside containers +though. + +While QEMU does its best to emulate atomic operations properly +differences between the host and guest memory models can cause issues +for software that makes assumptions about the memory model. =20 QEMU was conceived so that ultimately it can emulate itself. Although it is not very useful, it is an important test to show the power of the --=20 2.47.2