linux-kernel - Re: [Xen-devel] [PATCH 2/3] xen/pv-on-hvm kexec: rebind virqs to existing eventchannel ports

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Message-ID: <20110809185100.GA19520@dumpdata.com>
Date:	Tue, 9 Aug 2011 14:51:00 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Olaf Hering <olaf@...fle.de>
Cc:	Ian Campbell <Ian.Campbell@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] [PATCH 2/3] xen/pv-on-hvm kexec: rebind virqs to
 existing eventchannel ports

On Tue, Aug 09, 2011 at 05:28:06PM +0200, Olaf Hering wrote:
> On Tue, Aug 09, Ian Campbell wrote:
> 
> > On Thu, 2011-08-04 at 17:20 +0100, Olaf Hering wrote:
> > > During a kexec boot some virqs such as timer and debugirq were already
> > > registered by the old kernel.  The hypervisor will return -EEXISTS from
> > > the new EVTCHNOP_bind_virq request and the BUG in bind_virq_to_irq()
> > > triggers.  Catch the -EEXISTS error and loop through all possible ports to find
> > > what port belongs to the virq/cpu combo.
> > 
> > Would it be better to proactively just query the status of all event
> > channels early on, like you do in find_virq, and setup the irq info
> > structures as appropriate? Rather than waiting for an -EEXISTS I mean.

We only create those structures when the IRQ handler is setup. And since
this is a new kernel, the irq_get_handler_data(irq) won't be present.
> 
> Now that I read that again more carefully: 
> No idea if thats possible, I will leave that answer to Jeremy/Konrad.

But we could an optimization. The find_virq does a search every time
from 0->NR_EVENTS. Perhaps we can also check the xen_irq_list_head
to skip over the event channels we have already created?

Something like this:

   bool skip = false;
   list_for_each_entry(info, &xen_irq_list_head, list)
   if (info->evtchn == port && info->cpu == cpu) {
        skip=true;
        break;
    }
    if (skip)
        continue

    .. snip..
    and here is the EVTCHNOP_status hypercall.
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