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From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
	kvm@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>,
	Marc Zyngier <maz@kernel.org>,
	bigeasy@linutronix.de, linux-kernel@vger.kernel.org,
	rostedt@goodmis.org, linux-mips@vger.kernel.org,
	Paul Mackerras <paulus@ozlabs.org>,
	will@kernel.org, joel@joelfernandes.org, tglx@linutronix.de,
	torvalds@linux-foundation.org, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 4/5] kvm: Replace vcpu->swait with rcuwait
Date: Thu, 23 Apr 2020 11:19:11 +0200	[thread overview]
Message-ID: <20200423091911.GP20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <f07f6f55-9339-04b0-3877-d3240abd6d9c@redhat.com>

On Thu, Apr 23, 2020 at 10:57:57AM +0200, Paolo Bonzini wrote:
> On 23/04/20 10:41, Marc Zyngier wrote:
> >>  
> >> -	if (swait_active(kvm_arch_vcpu_wq(vcpu)))
> >> +	if (rcu_dereference(kvm_arch_vpu_get_wait(vcpu)) != NULL)
> > This doesn't compile (wrong function name, and rcu_dereference takes a
> > variable). But whatever it would do if we fixed it looks dodgy. it isn't
> > the rcuwait structure that you want to dereference, but rcuwait->task
> > (we are checking whether we are called because we are blocking or being
> > preempted).
> > 
> 
> Yes, I agree.  Replacing swait with rcuwait is all good, but please make
> the API look the same first.  Just like you added prepare_to_rcuwait and
> finish_rcuwait, let's add rcuwait_active as well.
> 
> Actually let's do it like this:
> 
> 1) Davidlohr, please post only patches 1-3 to "equalize" the swait and
> rcuwait APIs.
> 
> 2) Peter, please prepare a topic branch for those, or provide Acked-by

I don't think I have anything that conflicts with this, so sure, take
the whole thing through KVM.

For 1-3 (and I'll send a small niggle for 3 right after this):

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

I'll keep 5 as it is unrelated.
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Marc Zyngier <maz@kernel.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	tglx@linutronix.de, kvm@vger.kernel.org,
	Davidlohr Bueso <dbueso@suse.de>,
	torvalds@linux-foundation.org, bigeasy@linutronix.de,
	linux-kernel@vger.kernel.org, rostedt@goodmis.org,
	linux-mips@vger.kernel.org, Paul Mackerras <paulus@ozlabs.org>,
	joel@joelfernandes.org, will@kernel.org,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 4/5] kvm: Replace vcpu->swait with rcuwait
Date: Thu, 23 Apr 2020 11:19:11 +0200	[thread overview]
Message-ID: <20200423091911.GP20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <f07f6f55-9339-04b0-3877-d3240abd6d9c@redhat.com>

On Thu, Apr 23, 2020 at 10:57:57AM +0200, Paolo Bonzini wrote:
> On 23/04/20 10:41, Marc Zyngier wrote:
> >>  
> >> -	if (swait_active(kvm_arch_vcpu_wq(vcpu)))
> >> +	if (rcu_dereference(kvm_arch_vpu_get_wait(vcpu)) != NULL)
> > This doesn't compile (wrong function name, and rcu_dereference takes a
> > variable). But whatever it would do if we fixed it looks dodgy. it isn't
> > the rcuwait structure that you want to dereference, but rcuwait->task
> > (we are checking whether we are called because we are blocking or being
> > preempted).
> > 
> 
> Yes, I agree.  Replacing swait with rcuwait is all good, but please make
> the API look the same first.  Just like you added prepare_to_rcuwait and
> finish_rcuwait, let's add rcuwait_active as well.
> 
> Actually let's do it like this:
> 
> 1) Davidlohr, please post only patches 1-3 to "equalize" the swait and
> rcuwait APIs.
> 
> 2) Peter, please prepare a topic branch for those, or provide Acked-by

I don't think I have anything that conflicts with this, so sure, take
the whole thing through KVM.

For 1-3 (and I'll send a small niggle for 3 right after this):

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

I'll keep 5 as it is unrelated.

  reply	other threads:[~2020-04-23  9:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-22  4:07 [PATCH v3 -tip 0/5] kvm: Use rcuwait for vcpu blocking Davidlohr Bueso
2020-04-22  4:07 ` [PATCH 1/5] rcuwait: Fix stale wake call name in comment Davidlohr Bueso
2020-04-22  4:07 ` [PATCH 2/5] rcuwait: Let rcuwait_wake_up() return whether or not a task was awoken Davidlohr Bueso
2020-04-22  4:07 ` [PATCH 3/5] rcuwait: Introduce prepare_to and finish_rcuwait Davidlohr Bueso
2020-04-23  9:23   ` Peter Zijlstra
2020-04-22  4:07 ` [PATCH 4/5] kvm: Replace vcpu->swait with rcuwait Davidlohr Bueso
2020-04-22  4:07   ` Davidlohr Bueso
2020-04-22  8:32   ` Paolo Bonzini
2020-04-22  8:32     ` Paolo Bonzini
2020-04-22 10:14   ` Marc Zyngier
2020-04-22 10:14     ` Marc Zyngier
2020-04-23  8:41   ` Marc Zyngier
2020-04-23  8:41     ` Marc Zyngier
2020-04-23  8:57     ` Paolo Bonzini
2020-04-23  8:57       ` Paolo Bonzini
2020-04-23  9:19       ` Peter Zijlstra [this message]
2020-04-23  9:19         ` Peter Zijlstra
2020-04-23  9:26         ` Paolo Bonzini
2020-04-23  9:26           ` Paolo Bonzini
2020-04-22  4:07 ` [PATCH 5/5] sched/swait: Reword some of the main description Davidlohr Bueso
2020-05-01 18:22   ` [tip: sched/core] " tip-bot2 for Davidlohr Bueso
2020-04-22 11:33 ` [PATCH v3 -tip 0/5] kvm: Use rcuwait for vcpu blocking Peter Zijlstra

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