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([2001:b07:6468:f312:310b:68e5:c01a:3778]) by smtp.gmail.com with ESMTPSA id l10sm13553687wru.3.2020.08.08.05.00.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 08 Aug 2020 05:00:28 -0700 (PDT) Subject: Re: [PATCH v1 01/21] accel/tcg: Change interrupt/exception handling to remove implied BQL To: Robert Foley References: <20200805181303.7822-1-robert.foley@linaro.org> <20200805181303.7822-2-robert.foley@linaro.org> <4e678ed7-fc36-7918-ce9e-7a7e309c56df@redhat.com> From: Paolo Bonzini Message-ID: Date: Sat, 8 Aug 2020 14:00:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US 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 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/08 08:00:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: Richard Henderson , QEMU Developers , "Emilio G. Cota" , Peter Puhov , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 08/08/20 00:18, Robert Foley wrote: > 2) Another perhaps cleaner option is to add a new cpu class function > ->do_interrupt_locked. > This lets callers like *_cpu_exec_interrupt call to ->do_interrupt_locked > with lock held and solves the issue without resorting to conditional locking. > > Another benefit we could gain from this approach is to simplify our solution > overall by adding a common do_interrupt function. > > void cpu_common_do_interrupt(CPUState *cs) > { > CPUClass *cc = CPU_GET_CLASS(cpu); > qemu_mutex_lock_iothread(); > cc->do_interrupt_locked(cpu); > qemu_mutex_unlock_iothread(); > } > cc->do_interrupt would be set to cpu_common_do_interrupt by default > in cpu_class_init. > In other words, the base cpu class would handle holding the BQL for us, > and we would not need to implement a new *_do_interrupt function > for each arch. > > We are thinking that 2) would be a good option. Yes, it is. The only slight complication is that you'd have both ->do_interrupt and ->do_interrupt_locked so you probably should add some consistency check, for example /* * cc->do_interrupt_locked should only be needed if * the class uses cpu_common_do_interrupt. */ assert(cc->do_interrupt == cpu_common_do_interrupt || !cc->do_interrupt_locked); Therefore, a variant is to add ->do_interrupt_locked to ARMCPUClass and CRISCPUClass (target/avr/helper.c can just call avr_cpu_do_interrupt_locked, because that's the only value that cc->do_interrupt can have). Then ARM and CRIS can have a do_interrupt like you wrote above: void arm_do_interrupt(CPUState *cs) { ARMCPUClass *acc = ARM_CPU_GET_CLASS(cs); qemu_mutex_lock_iothread(); acc->do_interrupt_locked(cpu); qemu_mutex_unlock_iothread(); } with a small duplication between ARM and CRIS but on the other hand a simpler definition of the common CPUClass. Paolo