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([2001:b07:6468:f312:48f9:bea:a04c:3dfe]) by smtp.googlemail.com with ESMTPSA id k13sm7619520wri.6.2021.12.17.07.54.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Dec 2021 07:54:23 -0800 (PST) Message-ID: <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> Date: Fri, 17 Dec 2021 16:54:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: Possible nohz-full/RCU issue in arm64 KVM Content-Language: en-US To: Mark Rutland , Nicolas Saenz Julienne Cc: paulmck , maz , frederic , linux-kernel , rcu , Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel References: <70f112072d9496d21901946ea82832d3ed3a8cb2.camel@redhat.com> From: Paolo Bonzini In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211217_075426_138043_14A490D2 X-CRM114-Status: GOOD ( 11.21 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 12/17/21 15:38, Mark Rutland wrote: > For example kvm_guest_enter_irqoff() calls guest_enter_irq_off() which calls > vtime_account_guest_enter(), but kvm_guest_exit_irqoff() doesn't call > guest_exit_irq_off() and the call to vtime_account_guest_exit() is open-coded > elsewhere. Also, guest_enter_irq_off() conditionally calls > rcu_virt_note_context_switch(), but I can't immediately spot anything on the > exit side that corresponded with that, which looks suspicious. rcu_note_context_switch() is a point-in-time notification; it's not strictly necessary, but it may improve performance a bit by avoiding unnecessary IPIs from the RCU subsystem. There's no benefit from doing it when you're back from the guest, because at that point the CPU is just running normal kernel code. Paolo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel