[libvirt] [PATCH 1/2] conf: add disk cache tuning parameters after qemu

[Denis V. Lunev]

On 10/05/2016 10:43 AM, Nikolay Shirokovskiy wrote:
> adding cc
>
> On 26.09.2016 13:36, Nikolay Shirokovskiy wrote:
>>
>> On 26.09.2016 13:04, Peter Krempa wrote:
>>> On Mon, Sep 26, 2016 at 12:15:42 +0300, Nikolay Shirokovskiy wrote:
>>>> On 26.09.2016 12:01, Peter Krempa wrote:
>>> [...]
>>>
>>>> Sorry, I forget to write down the motivation.
>>>>
>>>> Internally qemu uses 3 orthogonal flags to configure disk cache. They
>>>> are exposed in interface too quite long time ago (29c4e2b). All-in-one
>>>> cache parameter that libvirt uses now do not provide all possible
>>>> values (5 vs 8). For example absent combination of direct + no flush (no sync)
>>>> is useful to speed up tests.
>>> Well, if there are useful combinations we can add them to the existing
>>> cache setting.
>>>
>>>> So I decided to provide new possibilities just as qemu does - keep
>>>> old parameter and use new ones to tune over.
>>> I don't think this is a good idea at all. It's very qemu specific and
>>> can be mapped to existing elements.
>>>
>>> Peter
>>>
>> Well up until now libvirt cache settings are exactly the same as the qemu ones. I thought
>> it would be inconsistent to intordocuce new name and then map internallly to 
>> qemu. Another point is that these 3 parameters are probably not that qemu specific.
>>
>> Nikolay
>>
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>>
the problem is that current modes are a little bit adhoc.
The describe non-trivial combination of 3 parameters,
which could be tuned on/off independently. That is why
it would be more clear to use the approach with separate
flags.

Den