linux-kernel - Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check

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Message-ID: <20160706075814.GF30921@twins.programming.kicks-ass.net>
Date:	Wed, 6 Jul 2016 09:58:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	xinhui <xinhui.pan@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org,
	virtualization@...ts.linux-foundation.org,
	linux-s390 <linux-s390@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, mpe@...erman.id.au,
	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@....com>, will.deacon@....com,
	boqun.feng@...il.com, Davidlohr Bueso <dave@...olabs.net>,
	schwidefsky@...ibm.com, Paolo Bonzini <pbonzini@...hat.com>,
	kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check

On Wed, Jul 06, 2016 at 02:46:34PM +0800, Wanpeng Li wrote:
> > SO it's easy for ppc to implement such interface. Note that yield_count is
> > set by powerVM/KVM.
> > and only pSeries can run a guest for now. :)
> >
> > I also review x86 related code, looks like we need add one hyer-call to get
> > such vcpu preemption info?
> 
> There is no such stuff to record lock holder in x86 kvm, maybe we
> don't need to depend on PLE handler algorithm to guess it if we can
> know lock holder vCPU directly.

x86/kvm has vcpu->preempted to indicate if a vcpu is currently preempted
or not. I'm just not sure if that is visible to the guest or how to make
it so.