linux-kernel - Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb

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Date:	Tue, 01 May 2012 17:36:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>, mingo@...e.hu,
	jeremy@...p.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	x86@...nel.org, vatsa@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others

On Tue, 2012-05-01 at 18:31 +0300, Avi Kivity wrote:
> On 05/01/2012 05:59 PM, Peter Zijlstra wrote:
> > On Tue, 2012-05-01 at 15:12 +0300, Avi Kivity wrote:
> > > local_irq_save() is a stronger version or rcu_read_lock()
> >
> > Not so, local_irq_save() doesn't at all stop regular RCU grace periods,
> > things like preemptible rcu can be driven from rcu_read_unlock().
> >
> > Note that this is the reason call_rcu_sched() exists and is used in this
> > case.
> 
> Ah, thanks for the correction.  I'll read some more about the _sched
> variants.

Basically:

 rcu_read_{,un}lock_sched() -- aka preempt_{en,dis}able()
 call_rcu_sched()
 synchronize_rcu_sched() -- aka synchronize_sched();

Define an RCU variant where each cpu has to have scheduled at least once
to complete a grace period.


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