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

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Message-ID: <20130501145753.GB6614@phenom.dumpdata.com>
Date:	Wed, 1 May 2013 10:57:53 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	"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, 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).
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