[Mesa-dev] [PATCH] gallium/radeon: add a new HUD query for the number of mapped buffers

[Christian König]

Am 24.01.2017 um 11:44 schrieb Samuel Pitoiset:
>
>
> On 01/24/2017 11:38 AM, Nicolai Hähnle wrote:
>> On 24.01.2017 11:34, Samuel Pitoiset wrote:
>>>
>>>
>>> On 01/24/2017 11:31 AM, Nicolai Hähnle wrote:
>>>> On 24.01.2017 11:25, Samuel Pitoiset wrote:
>>>>> On 01/24/2017 07:39 AM, Michel Dänzer wrote:
>>>>>> On 24/01/17 05:44 AM, Samuel Pitoiset wrote:
>>>>>>> Useful when debugging applications which map too much VRAM.
>>>>>>
>>>>>> Is the number of mapped buffers really useful, as opposed to the 
>>>>>> total
>>>>>> size of buffer mappings? Even if it was the latter though, it 
>>>>>> doesn't
>>>>>> show which mappings are for BOs in VRAM vs GTT, does it? Also, even
>>>>>> the
>>>>>> total size of mappings of BOs currently in VRAM doesn't directly
>>>>>> reflect
>>>>>> the pressure on the CPU visible part of VRAM — only the BOs which 
>>>>>> are
>>>>>> actively being accessed by the CPU contribute to that.
>>>>>
>>>>> It's actually useful to know the number of mapped buffers, but 
>>>>> maybe it
>>>>> would be better to have two separate counters for GTT and VRAM.
>>>>> Although
>>>>> the number of mapped buffers in VRAM is most of the time very high
>>>>> compared to GTT AFAIK.
>>>>>
>>>>> I will submit in a follow-up patch, something which reduces the 
>>>>> number
>>>>> of mapped buffers in VRAM (when a BO has been mapped only once). And
>>>>> this new counter helped me.
>>>>
>>>> Michel's point probably means that reducing the number/size of mapped
>>>> VRAM buffers isn't actually that important though.
>>>
>>> It seems useful for apps which map more than 256MB of VRAM.
>>
>> True, if all of that range is actually used by the CPU (which may well
>> happen, of course). If I understand Michel correctly (and this was news
>> to me as well), if 1GB of VRAM is mapped, but only 64MB of that are
>> regularly accessed by the CPU, then the kernel will migrate all of the
>> rest into non-visible VRAM.
>
> And this can hurt us, for example DXMD maps over 500MB of VRAM. And a 
> bunch of BOs are only mapped once.

But when they are mapped once that won't be a problem.

Again as Michel noted when a VRAM buffer is mapped it is migrated into 
the visible parts of VRAM on access, not on mapping.

In other words you can map all your VRAM buffers and keep them mapped 
and that won't hurt anybody.

Regards,
Christian.

>
>>
>> Nicolai
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