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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id q15sm13289063edt.95.2020.11.18.06.51.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Nov 2020 06:51:45 -0800 (PST) To: Eduardo Habkost References: <20201118102936.25569-1-cfontana@suse.de> <20201118102936.25569-9-cfontana@suse.de> <20201118124845.GC1509407@habkost.net> <6093de34-807d-3840-5402-4769385dd894@suse.de> <8f829e99-c346-00bc-efdd-3e6d69cfba35@redhat.com> <20201118143643.GF1509407@habkost.net> From: Paolo Bonzini Subject: Re: [RFC v3 8/9] module: introduce MODULE_INIT_ACCEL_CPU Message-ID: Date: Wed, 18 Nov 2020 15:51:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201118143643.GF1509407@habkost.net> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/18 00:38:29 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Laurent Vivier , Bruce Rogers , Thomas Huth , Stefano Stabellini , Paul Durrant , Olaf Hering , Jason Wang , Marcelo Tosatti , qemu-devel@nongnu.org, Peter Xu , Dario Faggioli , Roman Bolshakov , Cameron Esfahani , Colin Xu , Wenchao Wang , Anthony Perard , haxm-team@intel.com, Sunil Muthuswamy , Richard Henderson , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Claudio Fontana Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 18/11/20 15:36, Eduardo Habkost wrote: > On Wed, Nov 18, 2020 at 03:05:42PM +0100, Paolo Bonzini wrote: >> On 18/11/20 14:48, Claudio Fontana wrote: >>> On 11/18/20 1:48 PM, Eduardo Habkost wrote: >>>> I don't get why we would use a new module initialization level >>> >>> To have a clear point in time after which all accelerator interface initialization is done. >>> It avoids to have to hunt down the registration points spread around the code base. >>> I'd turn it around, why not? >> >> I see two disadvantages: >> >> 1) you have to hunt down accel_cpu_inits instead of looking at accelerator >> classes. :) >> >> 2) all callbacks have an "if (*_enabled())" around the actual meat. Another >> related issue is that usually the module_call_init are unconditional. >> >> I think the idea of using module_call_init is good however. What about: >> >> static void kvm_cpu_accel_init(void) >> { >> x86_cpu_accel_init(&kvm_cpu_accel); > > What do you expect x86_cpu_accel_init() to do? I don't know, the same that it was doing in Claudio's patches. :) He had if (kvm_enabled()) { x86_cpu_accel_init(&kvm_cpu_accel); } and I'm calling only the function that is registered on the enabled accelerator. > I don't understand why a separate module init level is necessary > here. Because you must call accel_register_call after the TYPE_KVM type has been registered, or object_class_by_name fails: void accel_register_call(const char *qom_type, void (*fn)(void)) { AccelClass *acc = ACCEL_CLASS(object_class_by_name(qom_type)); acc->setup_calls = g_slist_append(acc->setup_calls, (void *)fn); } The alternative is to store the (type, function) tuple directly, with the type as a string. Then you can just use type_init. > Making sure module_call_init() is called at the correct moment is > not easier or safer than just making sure accel_init_machine() > (or another init function you create) is called at the correct > moment. Since there is a way to do it without a new level, that would of course be fine for me too. Let me explain however why I think Claudio's design had module_call_init() misplaced and what the fundamental difference is. The basic phases in qemu_init() are: - initialize stuff - parse command line - create machine - create accelerator - initialize machine - create devices - start with a mess of other object creation sprinkled between the various phases (but we don't care about those). What I object to, is calling module_call_init() after the "initialize stuff" phase. Claudio was using it to call the function directly, so it had to be exactly at "create accelerator". This is different from all other module_call_init() calls, which are done very early. With the implementation I sketched, accel_register_call must still be done after type_init, so there's still an ordering constraint, but all it's doing is registering a callback in the "initialize stuff" phase. Thanks, Paolo