WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] Re: [PATCH 1/5] xen: events: use irq_alloc_desc(_at) ins

To: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH 1/5] xen: events: use irq_alloc_desc(_at) instead of open-coding an IRQ allocator.
From: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Date: Thu, 28 Oct 2010 14:57:53 +0200
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Delivery-date: Thu, 28 Oct 2010 05:59:34 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <alpine.DEB.2.00.1010281303330.1407@kaball-desktop>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Organization: Eikelenboom IT services
References: <1288023736.11153.40.camel@xxxxxxxxxxxxxxxxxxxxxx> <1288023813-31989-1-git-send-email-ian.campbell@xxxxxxxxxx> <20101025173522.GA5590@xxxxxxxxxxxx> <4CC60CB7.3070005@xxxxxxxx> <20101026141739.GA9557@xxxxxxxxxxxx> <4CC70583.2050503@xxxxxxxx> <20101026170841.GA10708@xxxxxxxxxxxx> <alpine.DEB.2.00.1010281303330.1407@kaball-desktop>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Hello Stefano,

Thursday, October 28, 2010, 2:43:12 PM, you wrote:

> On Tue, 26 Oct 2010, Konrad Rzeszutek Wilk wrote:
>> > In that case we should use dynamic allocation for everything.  Or try to
>> > work out distinct irq ranges for different interrupts if you really want
>> > to keep irq==gsi.
>> 
>> Some little alarm bells are ringing in the back of my head about irq != gsi.
>> 
>> I think the issue was the permission. When a PCI device is allocated to the
>> PV guest, we do a bunch of xc_* calls to allow the domain to use the BARs
>> and the IRQ. I believe when the guest boots and tries to map the
>> event channel with the physical IRQ, one of the arguments is that GSI. And
>> if we provide a bogus GSI, well, we won't get the INTx to the guest.
>> 
>> As you mentioned, Stefano's patch add a new element to the tuple that can
>> contain the GSI value. At which point we can make the guest IRQ != GSI,
>> as long as we can contain the <gsi, event channel> mapping present so
>> that for the hypercalls we can give it the right GSI.
>> 
>> The MSI/MSI-X use a completly different mechanism that does not all
>> of this complication, so we are OK with that.
>> 
>> .. snip ..
>> 
>> > d) dynamically allocate all irqs for all event channel types.
>> 
>> <nods> Ok, you sold me on this idea.
>> 


> Even though dynamic allocation might seem possible for both pirqs and
> irqs, there are some severe limitations:


> - Xen won't allocate pirq numbers lower than 16 (probably because it
> expects pirq == gsi for the first 16 gsi), so it might run out
> of pirqs if we ask Xen to always choose the pirq number for us.  As a
> consequence it is safer to keep using pirq == gsi, at least for the
> first 16 gsis. This limitation should probably be fixed in Xen, but we
> need to support older hypervisors so we cannot rely on the fix to be
> present.

I don't know if this discussion is for dom0 kernels only., if it is .. is that 
support of older hypervisors necessarily true ?

If i read the xen pvops wiki:
      NOTE! xen/stable-2.6.32.x versions after June 2010 (2.6.32.15 and newer) 
require at least Xen 4.0.1-rc2 or newer to work properly!
      xend and xenstored will fail to start if using those kernel versions with 
for example Xen 4.0.0.
      There's an issue with creating/using /dev/xen/ device nodes, which has 
been fixed in Xen 4.0.1-rc2 and newer versions.
      See this patch: 
http://xenbits.xen.org/xen-4.0-testing.hg?rev/0e1521f654f2 and discussion at: 
http://lists.xensource.com/archives/html/xen-devel/2010-06/msg01129.html for 
more information.

So a pvops dom0 kernel all ready seems to require a very recent hypervisor. So 
for a dom0 pvops kernel there has to be much less worry about support for older 
hypervisors for Xen guests it would only apply for pv domains ?
So this could perhaps also be the opportunity to change things ?

--
Sander



> - Linux expects irq == gsi, see arch/x86/kernel/acpi/boot.c:gsi_to_irq

>         /* Provide an identity mapping of gsi == irq
>          * except on truly weird platforms that have
>          * non isa irqs in the first 16 gsis.
>          */






-- 
Best regards,
 Sander                            mailto:linux@xxxxxxxxxxxxxx


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>