Re: [PATCH RFC 0/1] To add HMP interface to dump PCI MSI-X table/PBA

[Jason Wang <jasowang@redhat.com>]

在 2021/4/27 下午4:53, Dr. David Alan Gilbert 写道:
> * Dongli Zhang (dongli.zhang@oracle.com) wrote:
>>
>> On 4/22/21 11:01 PM, Jason Wang wrote:
>>> 在 2021/4/23 下午12:47, Dongli Zhang 写道:
>>>> This is inspired by the discussion with Jason on below patchset.
>>>>
>>>> https://urldefense.com/v3/__https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg09020.html__;!!GqivPVa7Brio!KbGQZW5lq3JZ60k12NuWZ6Th1lT6AwmBTF0pBgoWUKKQ4-2UhdW57PtvXUN5XQnZ2NU$
>>>>
>>>> The new HMP command is introduced to dump the MSI-X table and PBA.
>>>>
>>>> Initially, I was going to add new option to "info pci". However, as the
>>>> number of entries is not determined and the output of MSI-X table is much
>>>> more similar to the output of hmp_info_tlb()/hmp_info_mem(), this patch
>>>> adds interface for only HMP.
>>>>
>>>> The patch is tagged with RFC because I am looking for suggestions on:
>>>>
>>>> 1. Is it fine to add new "info msix <dev>" command?
>>>
>>> I wonder the reason for not simply reusing "info pci"?
>> The "info pci" will show PCI data for all devices and it does not accept any
>> argument to print for a specific device.
>>
>> In addition, the "info pci" relies on qmp_query_pci(), where this patch will not
>> implement the interface for QMP considering the number of MSI-X entries is not
>> determined.
>>
>> Suppose we have 10 NVMe (emulated by QEMU with default number of queues), we
>> will have about 600+ lines of output.
>  From an HMP perspective I'm happy, so:
>
> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
> but since I don't know much about MSI I'd like to see Jason's reply.


I think we'd better have more information, e.g the device can optionally 
report how the MSI-X vector is used.

Virtio-pci could be the first user for this.


>
> Adding an optional option to 'info pci' to limit to one device would be easy
> though; that bit is probably easier than adding a new command.


One interesting point is that MSI could be extended for other bus, (e.g 
MMIO). So "info msi" should be better I guess.


> Figuring out the QMP representation of your entries might be harder -
> and if this is strictly for debug, probably not worth it?


I think so.

Thanks


>
> Dave
>
>
>> Dongli Zhang
>>
>>>
>>>> 2. Is there any issue with output format?
>>>
>>> If it's not for QMP, I guess it's not a part of ABI so it should be fine.
>>>
>>>
>>>> 3. Is it fine to add only for HMP, but not QMP?
>>>
>>> I think so.
>>>
>>> Thanks
>>>
>>>
>>>> Thank you very much!
>>>>
>>>> Dongli Zhang
>>>>
>>>>
>>>>