[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] pci-assign can not work
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] pci-assign can not work |
Date: |
Fri, 16 Mar 2012 09:27:40 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2012-03-16 03:38, Wen Congyang wrote:
> At 03/15/2012 06:21 PM, Wen Congyang Wrote:
>> Hi all
>>
>> When I use pci-assign, I meet the following error:
>>
>> Failed to assign irq for "hostdev0": Input/output error
>> Perhaps you are assigning a device that shares an IRQ with another device?
>>
>> Is it a bug or I miss something?
>
> Hi, Jan
>
> This problem is caused by your patch:
> commit 6919115a8715c34cd80baa08422d90496f11f5d7
> Author: Jan Kiszka <address@hidden>
> Date: Thu Mar 8 11:10:27 2012 +0100
>
> pci_assign: Flip defaults of prefer_msi and share_intx
>
> INTx sharing is a bit more expensive than exclusive host interrupts, but
> this channel is not supposed to be used for high-performance scenarios
> anyway. Modern devices support MSI/MSI-X and do not depend on using INTx
> under critical workload, real old devices do not support INTx sharing
> anyway.
>
> For those in the middle, the user experience is much better if they just
> work even when IRQ sharing is required. If there is nothing to share,
> share_intx=off can still be applied as tuning parameter.
>
> With INTx sharing as default, the primary reason for prefer_msi=on is
> gone. Make it default off, specifically as it is known to cause troubles
> with devices that have incomplete/broken MSI support or otherwise
> stumble if host IRQ configuration does not match guest driver
> expectation.
>
> Acked-by: Alex Williamson <address@hidden>
> Signed-off-by: Jan Kiszka <address@hidden>
> Signed-off-by: Marcelo Tosatti <address@hidden>
>
> If I revert this commit. qemu can work.
>
This should be "solvable" by passing prefer_msi=on to the pci-assign
device, or likely by updating your host kernel to latest kvm.git (to
enable INTx sharing).
Hmm, unfortunate. We needed a conditional default for the prefer_msi
property here. If INTx sharing doesn't work for some reason AND the user
did not ask for disabling the host-side MSI usage, we should fall back
to it again.
Markus, is there some easy way to find out if a specific qdev property
was set due to a command line switch or was defined by the default value?
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux