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Re: [libvirt] [PATCH 3/4] domain_conf: Add support for iothreads in disk definition



On 08/26/2014 06:42 PM, John Ferlan wrote:
> 
> 
> On 08/26/2014 12:04 PM, Ján Tomko wrote:
>> On 08/26/2014 02:38 AM, John Ferlan wrote:
>>> Add a new disk "driver" attribute "iothread" to be parsed as the thread
>>> number for the disk to use. In order to more easily facilitate the usage
>>> and configuration of the iothread, a "zero" for the attribute indicates
>>> iothreads are not supported for the device and a positive value indicates
>>> the specific thread to try and use.
>>>
>>> Signed-off-by: John Ferlan <jferlan redhat com>
>>> ---
>>>  docs/formatdomain.html.in     |  8 ++++++++
>>>  docs/schemas/domaincommon.rng | 13 +++++++++++++
>>>  src/conf/domain_conf.c        | 24 +++++++++++++++++++++++-
>>>  src/conf/domain_conf.h        |  2 ++
>>>  4 files changed, 46 insertions(+), 1 deletion(-)
>>>
>>
>>> @@ -11968,6 +11980,14 @@ virDomainDefParseXML(xmlDocPtr xml,
>>>              goto error;
>>>          }
>>>          def->iothreads = count;
>>> +
>>> +        /* Create a bitmap for inuse threads - noting that entries are
>>> +         * numbered 1..def->iothreads since 0 (zero) iothreads means
>>> +         * nothing and assigning a disk to an IOThread requires at least a
>>> +         * thread# > 0 since a zero would indicate no IOThread for the disk
>>> +         */
>>> +        if (!(def->iothreadmap = virBitmapNew(def->iothreads+1)))
>>> +            goto error;
>>>      }
>>
>> Do you plan to do multiple disks on a single iothread in the followup patches?
>> Or is that a configuration that doesn't make sense?
>>
> 
> I would say it doesn't make sense and from the bz I have the comment is
> "2. 1 IOThread per device" (bz 1101574 if you care to read although it's
> mostly private comments though which is why I didn't put it in the patches).
> 

I was wondering what's up with all the private comments.

Hopefully I can share the bit you're quoting:
 There are basically two ways to use IOThreads:
1. 1 or maybe 2 IOThreads per host CPU
2. 1 IOThread per device

For usage 1), can you just add some <iothreads> to the domain XML and they
will automatically be used, or do you need to 'bind' the specific disk devices
to them?

Jan

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