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] IRQ SMP affinity problems in domU with vcpus > 4 on HP P

To: "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>, "He, Qing" <qing.he@xxxxxxxxx>
Subject: RE: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)
From: "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
Date: Fri, 16 Oct 2009 22:54:36 +0800
Accept-language: en-US
Acceptlanguage: en-US
Cc: "Cinco, Dante" <Dante.Cinco@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Delivery-date: Fri, 16 Oct 2009 07:55:14 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <706158FABBBA044BAD4FE898A02E4BC201C9BD840C@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
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>
References: <20091016023411.GA9650@ub-qhe2> <C6FDD334.17971%keir.fraser@xxxxxxxxxxxxx> <706158FABBBA044BAD4FE898A02E4BC201C9BD837A@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20091016082455.GH23672@ub-qhe2> <706158FABBBA044BAD4FE898A02E4BC201C9BD83AF@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20091016083445.GI23672@ub-qhe2> <706158FABBBA044BAD4FE898A02E4BC201C9BD83C6@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20091016090139.GJ23672@ub-qhe2> <706158FABBBA044BAD4FE898A02E4BC201C9BD840C@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcpOPi4Q9UlUI8ufS5qQ1CJSqDysQAAAM40gAAsf3SA=
Thread-topic: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)
Attached this new one which should eliminate the race ultimately. 
Xiantao 

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Zhang, Xiantao
Sent: Friday, October 16, 2009 5:50 PM
To: He, Qing
Cc: Cinco, Dante; xen-devel@xxxxxxxxxxxxxxxxxxx; Keir Fraser
Subject: RE: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP 
ProLiant G6 with dual Xeon 5540 (Nehalem)

He, Qing wrote:
> On Fri, 2009-10-16 at 16:35 +0800, Zhang, Xiantao wrote:
>> He, Qing wrote:
>>> On Fri, 2009-10-16 at 16:22 +0800, Zhang, Xiantao wrote:
>>>> He, Qing wrote:
>>>>> On Fri, 2009-10-16 at 15:32 +0800, Zhang, Xiantao wrote:
>>>>>> According to the description, the issue should be caused by lost
>>>>>> EOI write for the MSI interrupt and leads to permanent interrupt
>>>>>> mask. There should be a race between guest setting new vector and
>>>>>> EOIs old vector for the interrupt.  Once guest sets new vector
>>>>>> before it EOIs the old vector, hypervisor can't find the pirq
>>>>>> which corresponds old vector(has changed
>>>>>> to new vector) , so also can't EOI the old vector forever in
>>>>>> hardware level. Since the corresponding vector in real processor
>>>>>> can't be EOIed, so system may lose all interrupts and result the
>>>>>> reported issues ultimately.
>>>>> 
>>>>>> But I remembered there should be a timer to handle this case
>>>>>> through a forcible EOI write to the real processor after timeout,
>>>>>> but seems it doesn't function in the expected way.
>>>>> 
>>>>> The EOI timer is supposed to deal with the irq sharing problem,
>>>>> since MSI doesn't share, this timer will not be started in the
>>>>> case of MSI.
>>>> 
>>>> That maybe a problem if so. If a malicious/buggy guest won't EOI
>>>> the MSI vector, so host may hang due to lack of timeout mechanism?
>>> 
>>> Why does host hang? Only the assigned interrupt will block, and
>>> that's exactly what the guest wants :-)
>> 
>> Hypervisor shouldn't EOI the real vector until guest EOI the
>> corresponding virtual vector , right ?  Not sure.:-)
> 
> Yes, it is the algorithm used today.

So it should be still a problem. If guest won't do eoi, host can't do eoi also, 
and leads to system hang without timeout mechanism. So we may need to introduce 
a timer for each MSI interrupt source to avoid hanging host, Keir? 

> After reviewing the code, if the guest really does something like
> changing affinity within the window between an irq fire and eoi,
> there is indeed a problem, attached is the patch. Although I kinda
> doubt it, shouldn't desc->lock in guest protect and make these two
> operations mutual exclusive.

We shouldn't let hypervisor do real EOI before guest does the correponding 
virtual EOI, so this patch maybe have a correctness issue. :-)

Attached the fix according to my privious guess, and it should fix the issue. 

Xiantao

Attachment: fix-irq-affinity-msi3.patch
Description: fix-irq-affinity-msi3.patch

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
<Prev in Thread] Current Thread [Next in Thread>