From: Paolo Bonzini <pbonzini@redhat.com>
To: Mark Rutland <mark.rutland@arm.com>,
Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: paulmck <paulmck@kernel.org>, maz <maz@kernel.org>,
frederic <frederic@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
rcu <rcu@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: Possible nohz-full/RCU issue in arm64 KVM
Date: Fri, 17 Dec 2021 16:54:22 +0100 [thread overview]
Message-ID: <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> (raw)
In-Reply-To: <Ybyg1r/Q6EfeuXGV@FVFF77S0Q05N>
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
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next prev parent reply other threads:[~2021-12-17 15:54 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 11:51 Possible nohz-full/RCU issue in arm64 KVM Nicolas Saenz Julienne
2021-12-17 13:21 ` Mark Rutland
2021-12-17 14:15 ` Nicolas Saenz Julienne
2021-12-17 14:38 ` Mark Rutland
2021-12-17 15:54 ` Paolo Bonzini [this message]
2021-12-17 16:07 ` Paul E. McKenney
2021-12-17 16:20 ` Nicolas Saenz Julienne
2021-12-17 16:43 ` Paul E. McKenney
2021-12-17 16:34 ` Paolo Bonzini
2021-12-17 16:45 ` Paul E. McKenney
2021-12-17 17:02 ` Paolo Bonzini
2021-12-17 17:12 ` Paul E. McKenney
2021-12-17 17:23 ` Paolo Bonzini
2021-12-17 17:47 ` Paul E. McKenney
2022-01-04 16:39 ` Mark Rutland
2022-01-04 17:07 ` Paolo Bonzini
2022-01-11 11:32 ` Nicolas Saenz Julienne
2022-01-11 12:23 ` Mark Rutland
2021-12-17 14:51 ` Paolo Bonzini
2021-12-20 14:28 ` Marc Zyngier
2021-12-20 16:10 ` Frederic Weisbecker
2022-01-04 13:24 ` Mark Rutland
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