We have check the sematic of GL_DYANMIC_DRAW,

seems that it the Skia usage of GZL_DYNAMIC_DRAW is wrong.

 

Thanks

Zou Nanhai

From: Zou, Nanhai [mailto:nanhai.zou@intel.com]
Sent: Tuesday, July 24, 2012 11:25 AM
To: mesa3d-dev (Mesa3d-dev@lists.sourceforge.net)
Cc: Versace, Chad; Ian Romanick (idr@freedesktop.org)
Subject: [Mesa3d-dev] Correct behavior of GL_DYNAMIC_DRAW in glBufferData?

 

Hi,

         I have notice that in current driver implementation.

When GL_DYNAMIC_DRAW flag is set in glBufferData, driver will not upload data to

Graphics memory.

Instead it will upload the _entire_ vertex/index buffer when glDrawElements/glDrawArray was called.

 

This sometimes brings a huge bottleneck ,

e.g. in Skia.

 

Skia allocate a 256k vertexdata buffer and a 64k indexdata buffer as pools, and use glBufferData to upload the pools.

 

Most of the Skia draw operations will only use a few vertexes in the pool, but driver will upload the _entire_

buffer each operation.

 

This becomes No 1 bottleneck for Skia bench with GPU.

 

I have tested if reduce the pool size to 1k, many tests in Skia bench get 3x to >10x performance improvement…

 

Per my understanding. Even GL_DYNAMIC_DRAW is set in glBufferData, driver should not copy the entire buffer

When glDrawElements/glDrawArray is called, it should copy only used vertex/index.

 

Otherwise this is too heavy in Skia like usage scenario.

 

Thanks

Zou Nanhai