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Re: [libvirt] [PATCH] rng: tighten up domain <controller> schema



On 04/19/2013 11:25 AM, Laine Stump wrote:
> On 04/19/2013 04:32 AM, Osier Yang wrote:
>> On 18/04/13 19:59, Laine Stump wrote:
>>> On 04/18/2013 07:27 AM, Osier Yang wrote:
>>>> On 18/04/13 19:16, Laine Stump wrote:
>>>>> On 04/18/2013 05:41 AM, Martin Kletzander wrote:
>>>>>> On 04/18/2013 11:05 AM, Osier Yang wrote:
>>>>>>> On 18/04/13 17:00, Martin Kletzander wrote:
>>>>>>>> On 04/18/2013 10:54 AM, Osier Yang wrote:
>>>>>>>>> On 18/04/13 16:42, Martin Kletzander wrote:
>>>>>>>>>> On 04/18/2013 06:36 AM, Laine Stump wrote:
>>>>>>>>>>> The rng schema for <controller> had been non-specific about
>>>>>>>>>>> which
>>>>>>>>>>> types of controllers allowed which models, and also allowed the
>>>>>>>>>>> num_queues attribute (since that hasn't been released yet,
>>>>>>>>>>> should we
>>>>>>>>>>> rename it to "numQueues"?)
>>>>>>>>>> Since there's still time (the commit with that is
>>>>>>>>>> v1.0.4-65-gd4bf0a9), I
>>>>>>>>>> think we should rename it ASAP since we are using camelCase for
>>>>>>>>>> all the
>>>>>>>>>> attribute names.
>>>>>>>>>>
>>>>>>>>>> Apart from that, the RNG with this patch is precise according to
>>>>>>>>>> the
>>>>>>>>>> documentation, so ACK.  I'll try to send the numQueues patch
>>>>>>>>>> to see
>>>>>>>>>> what
>>>>>>>>>> others think.
>>>>>>>>> I guess you mean multiple queues support for virtio network?
>>>>>>>>> Regardless of which style we will use finally, FYI, 
>>>>>>>>> "num_queues" is
>>>>>>>>> used for disk.. Personally I'm fine with either, because we
>>>>>>>>> already
>>>>>>>>> use both across.
>>>>>>>>>
>>>>>>>> Yes, I meant the virtio-scsi num_queues.  As we're trying not to
>>>>>>>> use
>>>>>>>> underscores in XML, I hope we can still switch it.  I haven't
>>>>>>>> found any
>>>>>>>> other num_queues anywhere in the code.  Could you point me to the
>>>>>>>> commit
>>>>>>>> that uses that?  I'm sending the previously discussed patch in the
>>>>>>>> meantime.
>>>>>>>>
>>>>>>> Except the virtio-scsi num_queues, there is no other tag for
>>>>>>> multiple
>>>>>>> queue yet, we will need a patch to support multiple queue for the
>>>>>>> network,
>>>>>>> but it's not committed yet.
>>>>>>>
>>>>>>> It's fine to convert it now, 1.0.5 is not released yet. But is it
>>>>>>> deserved to
>>>>>>> do, we already have many tags with underscore, which can't be
>>>>>>> changed
>>>>>>> for back-compat.
>>>>>>>
>>>>>> I believe those attributes [1] were created by mistake, and kept only
>>>>>> because of backward compatibility.  I'm trying to be open-minded,
>>>>>> though, so I'm not forcing my patch in, but seeing it just as a
>>>>>> proposal.  Others may have different opinions and I'm willing to
>>>>>> discuss
>>>>>> that.  My first feeling, though, was that we should try to keep the
>>>>>> same
>>>>>> policy for as many of them as possible.  OTOH, I've mistaken the
>>>>>> underscore with a hyphen when I remembered what Daniel told me about
>>>>>> attributes [2].
>>>>> I had recalled DV saying something about underscores in the names a
>>>>> long
>>>>> time ago, and I recently asked about underscore vs. camelCase, and
>>>>> danpb
>>>>> said the same thing. (Personally I don't have a preference one way or
>>>>> the other, but if we really are trying to avoid them, now is our
>>>>> chance).
>>>> I'm fine with either keeping it or changing num_queues. For long
>>>> term consistence, I agreed with having a consistent naming style
>>>> is nice.
>>>>
>>>>> In the meantime, in other device types, we've tried to keep backend
>>>>> details like this pushed into a <driver> subelement when possible, to
>>>>> avoid polluting the main element (e.g. see the <driver> subelement of
>>>>> <interface>). Is it worth putting this numQueues attribute in a
>>>>> <driver>
>>>>> subelement too? Or am I just playing XML God?
>>>> Not sure if you mean the upcoming numQueues for interface. But for the
>>>> existing num_queues, it's for the virtio-scsi controller, putting it
>>>> in <driver>
>>>> doesn't reflect the purpose.
>>> But isn't it a backend implementation detail of the specific SCSI
>>> controller? In <interface> and <disk>, information that is specific to a
>>> particular backend (and isn't generally applicable to that type of
>>> device) is in the <driver> subelement.
>> This is the QEMU command line for a virtio-scsi disk: ("-device
>> virtio-scsi-pci"
>> is mapped to virtio-scsi controller in libvirt XML, with num_queues set):
>> <...>
>> -device virtio-scsi-pci,id=scsi0,num_queues=8,bus=pci.0,addr=0x3 \
>> -usb \
>> -drive file=/dev/HostVG/QEMUGuest1,if=none,id=drive-scsi0-0-0-0 \
>> -device
>> scsi-disk,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0
>> \
>> </...>
>>
>>
>> And this is the QEMU command line for a virtio disk (with event_idx set):
>> <...>
>> -drive
>> file=/var/lib/libvirt/images/f14.img,if=none,id=drive-virtio-disk0 \
>> -device
>> virtio-blk-pci,event_idx=on,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0
>> \
>> </...>
>>
>> This is the properties the QEMU device "scsi-disk" supports:
>>
>> % ./x86_64-softmmu/qemu-system-x86_64 -device scsi-disk,?
>> scsi-disk.drive=drive
>> scsi-disk.logical_block_size=blocksize
>> scsi-disk.physical_block_size=blocksize
>> scsi-disk.min_io_size=uint16
>> scsi-disk.opt_io_size=uint32
>> scsi-disk.bootindex=int32
>> scsi-disk.discard_granularity=uint32
>> scsi-disk.ver=string
>> scsi-disk.serial=string
>> scsi-disk.vendor=string
>> scsi-disk.product=string
>> scsi-disk.removable=on/off
>> scsi-disk.dpofua=on/off
>> scsi-disk.wwn=hex64
>> scsi-disk.channel=uint32
>> scsi-disk.scsi-id=uint32
>> scsi-disk.lun=uint32
>>
>> And the properties "virtio-blk-pci" device supports:
>>
>> % ./x86_64-softmmu/qemu-system-x86_64 -device virtio-blk-pci,?
>> virtio-blk-pci.class=hex32
>> virtio-blk-pci.ioeventfd=on/off
>> virtio-blk-pci.vectors=uint32
>> virtio-blk-pci.indirect_desc=on/off
>> virtio-blk-pci.event_idx=on/off
>> virtio-blk-pci.drive=drive
>> virtio-blk-pci.logical_block_size=blocksize
>> virtio-blk-pci.physical_block_size=blocksize
>> virtio-blk-pci.min_io_size=uint16
>> virtio-blk-pci.opt_io_size=uint32
>> virtio-blk-pci.bootindex=int32
>> virtio-blk-pci.discard_granularity=uint32
>> virtio-blk-pci.cyls=uint32
>> virtio-blk-pci.heads=uint32
>> virtio-blk-pci.secs=uint32
>> virtio-blk-pci.serial=string
>> virtio-blk-pci.config-wce=on/off
>> virtio-blk-pci.scsi=on/off
>> virtio-blk-pci.addr=pci-devfn
>> virtio-blk-pci.romfile=string
>> virtio-blk-pci.rombar=uint32
>> virtio-blk-pci.multifunction=on/off
>> virtio-blk-pci.command_serr_enable=on/off
>>
>> And the properties "virtio-scsi-pci" device supports:
>>
>> % ./x86_64-softmmu/qemu-system-x86_64 -device virtio-scsi-pci,?
>> virtio-scsi-pci.ioeventfd=on/off
>> virtio-scsi-pci.vectors=uint32
>> virtio-scsi-pci.indirect_desc=on/off
>> virtio-scsi-pci.event_idx=on/off
>> virtio-scsi-pci.hotplug=on/off
>> virtio-scsi-pci.param_change=on/off
>> virtio-scsi-pci.num_queues=uint32
>> virtio-scsi-pci.max_sectors=uint32
>> virtio-scsi-pci.cmd_per_lun=uint32
>> virtio-scsi-pci.addr=pci-devfn
>> virtio-scsi-pci.romfile=string
>> virtio-scsi-pci.rombar=uint32
>> virtio-scsi-pci.multifunction=on/off
>> virtio-scsi-pci.command_serr_enable=on/off
>>
>> We can put things like "ioeventfd", "event_idx" in the <driver>
>> subelement, is
>> because of the QEMU device used for disk supports it. But for a
>> virtio-scsi disk,
>> "num_queues" is supported in a separate device "virtio-scsi-pci"
>> instead.. That
>> means, from libvirt p.o.v,  things like "ioevent_idx" are for disk,
>> "num_queues"
>> is for the disk controller.
>>
>> Assuming that we put "num_queues" or "numQueues" in <driver>, then we
>> need
>> to find out the controller for disk when building QEMU command line,
>> and check
>> if it's virtio-scsi model, if not, error out, otherwise tell the
>> function to build the
>> controller device string that "num_queues" is specified, and what its
>> value is. Or
>> something similar but reversely (find out the disk associated with the
>> virtio-scsi
>> controller, check if num_queues is specified). This might be not the
>> exact process,
>> but it can show putting "num_queues" in <driver> is just a straight
>> wrong way to go...
> Wait. So you're saying that num_queues is a property of the *controller*
> and not of the individual disk, but you've put the config option in the
> <disk> rather than the <controller>? Why would you do that? If it's a
> property of the controller, put the tuning parameter in <controller>.
> Otherwise, what do you do when one <disk> is configured for
> num_queues=10 and another disk on the same controller is configured for
> num_queues=2?
>

Okay, I misunderstood what you said - you weren't saying that you had
put num_queues in the <disk> element (obviously - if I was able to
retain enough context in my brain to remember the beginning of the
thread, I would have known that :-P), but were instead suggesting that I
had meant the num_queues should go in the <driver> subelement of <disk>.
You misunderstood me (so we're even :-). What I was saying was that it
should go in the <driver> subelement of <controller>. I still stand by
that opinion.


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