linux-kernel - Re: [PATCH 8/9] xen/smp/pvhvm: Don't initialize IRQ

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Date:	Wed, 1 May 2013 14:25:16 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 8/9] xen/smp/pvhvm: Don't initialize IRQ_WORKER as we
 are using the native one.

On Mon, 29 Apr 2013, Konrad Rzeszutek Wilk wrote:
> On Fri, Apr 26, 2013 at 05:27:20PM +0100, Stefano Stabellini wrote:
> > On Tue, 16 Apr 2013, Konrad Rzeszutek Wilk wrote:
> > > There is no need to use the PV version of the IRQ_WORKER mechanism
> > > as under PVHVM we are using the native version. The native
> > > version is using the SMP API.
> > > 
> > > They just sit around unused:
> > > 
> > >   69:          0          0  xen-percpu-ipi       irqwork0
> > >   83:          0          0  xen-percpu-ipi       irqwork1
> > > 
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > 
> > Might be worth trying to make it work instead?
> > Is it just because we don't set the apic->send_IPI_* functions to the
> > xen specific version on PVHVM?
> > 
> 
> Right. We use the baremetal mechanism to do it. And it works fine.

OK, it works fine, but won't it generate many mores trap and emulate
cycles?


> > >  arch/x86/xen/smp.c | 13 ++++++++++++-
> > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> > > index 22c800a..415694c 100644
> > > --- a/arch/x86/xen/smp.c
> > > +++ b/arch/x86/xen/smp.c
> > > @@ -144,6 +144,13 @@ static int xen_smp_intr_init(unsigned int cpu)
> > >  		goto fail;
> > >  	per_cpu(xen_callfuncsingle_irq, cpu) = rc;
> > >  
> > > +	/*
> > > +	 * The IRQ worker on PVHVM goes through the native path and uses the
> > > +	 * IPI mechanism.
> > > +	 */
> > > +	if (xen_hvm_domain())
> > > +		return 0;
> > > +
> > >  	callfunc_name = kasprintf(GFP_KERNEL, "irqwork%d", cpu);
> > >  	rc = bind_ipi_to_irqhandler(XEN_IRQ_WORK_VECTOR,
> > >  				    cpu,
> > > @@ -167,6 +174,9 @@ static int xen_smp_intr_init(unsigned int cpu)
> > >  	if (per_cpu(xen_callfuncsingle_irq, cpu) >= 0)
> > >  		unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu),
> > >  				       NULL);
> > > +	if (xen_hvm_domain())
> > > +		return rc;
> > > +
> > >  	if (per_cpu(xen_irq_work, cpu) >= 0)
> > >  		unbind_from_irqhandler(per_cpu(xen_irq_work, cpu), NULL);
> > >  
> > > @@ -661,7 +671,8 @@ static void xen_hvm_cpu_die(unsigned int cpu)
> > >  	unbind_from_irqhandler(per_cpu(xen_callfunc_irq, cpu), NULL);
> > >  	unbind_from_irqhandler(per_cpu(xen_debug_irq, cpu), NULL);
> > >  	unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu), NULL);
> > > -	unbind_from_irqhandler(per_cpu(xen_irq_work, cpu), NULL);
> > > +	if (!xen_hvm_domain())
> > > +		unbind_from_irqhandler(per_cpu(xen_irq_work, cpu), NULL);
> > >  	xen_uninit_lock_cpu(cpu);
> > >  	xen_teardown_timer(cpu);
> > >  	native_cpu_die(cpu);
> > > -- 
> > > 1.8.1.4
> > > 
> 
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