linux-kernel - Re: [RFC PATCH 1/1] kvm: Note an RCU quiescent state on guest exit

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Message-ID: <f06ef91d-7f8c-4f69-8535-fee372766a7f@redhat.com>
Date: Fri, 12 Jul 2024 17:57:10 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Leonardo Bras <leobras@...hat.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
 Leonardo Bras <leobras.c@...il.com>, Sean Christopherson
 <seanjc@...gle.com>, Frederic Weisbecker <frederic@...nel.org>,
 Marcelo Tosatti <mtosatti@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] kvm: Note an RCU quiescent state on guest exit

On 7/11/24 01:18, Leonardo Bras wrote:
> What are your thoughts on above results?
> Anything you would suggest changing?

Can you run the test with a conditional on "!tick_nohz_full_cpu(vcpu->cpu)"?

If your hunch is correct that nohz-full CPUs already avoid 
invoke_rcu_core() you might get the best of both worlds.

tick_nohz_full_cpu() is very fast when there is no nohz-full CPU, 
because then it shortcuts on context_tracking_enabled() (which is just a 
static key).

Paolo