Nested servers frame rate

[Thomas Voß]

On Wed, Dec 18, 2013 at 10:01 AM, Daniel van Vugt
<daniel.van.vugt at canonical.com> wrote:
> The issue is in your response: "almost immediately" :)
>
> At present, "almost immediately" means waiting for a round trip. Whereas we
> can do better than that in theory, by pushing free buffers to the client as
> soon as they're available.
>

Fair, but I would like to see numbers on the roundtrip penalty you are
suspecting here, first :)

Cheers,

  Thomas

>
>
> On 18/12/13 16:58, Thomas Voß wrote:
>>
>> On Wed, Dec 18, 2013 at 9:43 AM, Daniel van Vugt
>> <daniel.van.vugt at canonical.com> wrote:
>>>
>>> At first glance, comparing frame rates between direct (single) and nested
>>> (double) server configurations reveals nothing unexpected...
>>>
>>> Full screen
>>> Direct (bypass) 2600
>>> Direct (bypass off) 2400
>>> Nested (bypass) 2450
>>> Nested (bypass off) 2330
>>>
>>> But for surfaces which can't be bypassed, something strange happens;
>>> nesting
>>> is faster!
>>>
>>> Windowed
>>> Nested 4890
>>> Direct 4400
>>>
>>> My best theory right now is that we're crippling Mir in the single server
>>> case due to:
>>> https://bugs.launchpad.net/mir/+bug/1253868
>>> and nesting provides a workaround for that problem by supplying extra
>>> levels
>>> of buffering.
>>
>>
>> Not sure I'm following your reasoning here: The bug states exactly the
>> opposite, i.e., additional buffering wouldn't help.
>> In addition: I do not see how a steady-state update scheme on the
>> client-side is a problem here. If there are more than two buffers
>> available per surface, the client almost immediately receives a new
>> buffer when it calls next_buffer. Sure, there is always only one
>> buffer in flight, but I cannot see why this would lead to the numbers
>> you are reporting here.
>>
>> Cheers,
>>
>>    Thomas
>>
>>>
>>> Can anyone else think why nested would sometimes be faster than not
>>> nested?
>>>
>>> - Daniel
>>>
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