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To: Gerd Hoffmann References: <20210610101553.943689-1-kraxel@redhat.com> <5953598.eXybCX72BP@pizza> <20210615050930.bmgup2axfr7sqvoa@sirius.home.kraxel.org> <2963309.4TrVdrBa0x@pizza> <20210616092815.rjznyjnvgrrfojq6@sirius.home.kraxel.org> <20210617053759.uibvdpu2wtq3fqwv@sirius.home.kraxel.org> From: Claudio Fontana Message-ID: <2be72be7-5c3f-e25d-fb84-cf58b573bf27@suse.de> Date: Thu, 17 Jun 2021 09:48:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20210617053759.uibvdpu2wtq3fqwv@sirius.home.kraxel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=195.135.220.28; envelope-from=cfontana@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -45 X-Spam_score: -4.6 X-Spam_bar: ---- X-Spam_report: (-4.6 / 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, NICE_REPLY_A=-0.17, RCVD_IN_DNSWL_MED=-2.3, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Michael S. Tsirkin" , Christian Schoenebeck , Greg Kurz , "qemu-devel@nongnu.org" , =?UTF-8?Q?Jos=c3=a9_Ricardo_Ziviani?= , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/17/21 7:37 AM, Gerd Hoffmann wrote: > Hi, > >>>> However, please correct me if I'm wrong, I understand that an accelerator as a >>>> module will add an overhead that some user won't be willing to pay. So, give >>>> them the option to have built-in accelerators seems a good idea. >>> >>> Modules add some overhead, yes, and there are surely use-cases where you >> >> Where do we expect the overhead to be, and of which nature? > > The dynamic linking needed then when loading the module adds a bit of > overhead (compared to static linked code). Increases qemu start time > a bit. > > On the other hand the start overhead can be reduced by modules, > specifically for the case that a module depends on shared libraries and > is *not* needed. With for example gtk being modular the gtk shared > libraries (plus indirect dependencies like pango, cairo etc) are only > loaded when you actually use gtk, whereas a non-modular build would load > them no matter what. Interesting observation. > > The code reorganization needed for modularization can add some overhead > too, when using function pointers instead of direct calls for example > (see QemuSpiceOps). That overhead doesn't go away when you do a > non-modular build though ... > > take care, > Gerd > Do we need to be able to unload modules that we previously loaded? Or is this not a realistic requirement? Thanks, Claudio