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To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Peter Maydell References: <159029353528.907.11982786579949073896.malonedeb@chaenomeles.canonical.com> From: Paolo Bonzini Message-ID: <36adab2a-bfb4-c60b-9a5b-5fe741d01325@redhat.com> Date: Mon, 25 May 2020 15:59:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/25 02:40:56 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: "Michael S. Tsirkin" , Mark Cave-Ayland , QEMU Developers , Bug 1880355 <1880355@bugs.launchpad.net>, Gerd Hoffmann , Stefan Hajnoczi , Laszlo Ersek Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 24/05/20 16:27, Philippe Mathieu-Daudé wrote: >> In an ideal world all our DMA devices would use some kind of common >> framework or design pattern so they didn't hog all the CPU >> and/or spend minutes with the BQL held if the guest requests >> an enormous-sized DMA. In practice many of them just have >> a simple "loop until the DMA transfer is complete" implementation... > Is this framework already implemented in the hidden dma-helpers.c? > > Apparently this file was written for BlockBackend, but the code seems > rather generic. The code is generic, see dma_buf_rw, but the asynchronous code is currently used only for block devices. Above a certain limit it would make sense to reuse them to perform dma_buf_rw in the thread pool. Paolo