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

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Message-ID: <alpine.DEB.2.02.1305011606320.5398@kaball.uk.xensource.com>
Date:	Wed, 1 May 2013 16:07:07 +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 Wed, 1 May 2013, Konrad Rzeszutek Wilk wrote:
> On Wed, May 01, 2013 at 02:25:16PM +0100, Stefano Stabellini wrote:
> > 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?
> 
> No idea. We can certainly make use of the PV IPI mechanism for IRQ_WORKER
> type mechaism but I would have to play with xentrace to get a good handle
> of what is involved (And how the v Posted interrupt thing affects this).
> 
> Right now that is something I can't do (buried in bugs).

OK
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