Radeon GTT size increase

[KBentley57]

I just compiled the 3.12 kernel and I noticed that during bootup the GTT video memory had been increased. I'm using an AMD 6970. on kernel 3.11.6, the GTT video memory size was set to 512M. Now I see it's set to 1G. Can anyone comment on the reasoning/benefits of the increase, and if all the upper end cards were increased?

[    3.589321] [drm] radeon kernel modesetting enabled.
[    3.590066] radeon 0000:01:00.0: VRAM: 2048M 0x0000000000000000 - 0x000000007FFFFFFF (2048M used)
[    3.590106] radeon 0000:01:00.0: GTT: 1024M 0x0000000080000000 - 0x00000000BFFFFFFF
[    3.590546] [drm] radeon: 2048M of VRAM memory ready
[    3.590581] [drm] radeon: 1024M of GTT memory ready.

[gradinaruvasile]

Its 1024 on the Trinity IGPs (at least on 7560D). I have no idea about benefits, it feels the same.

[bridgman]

Can anyone comment on the reasoning/benefits of the increase, and if all the upper end cards were increased?

Here's the text from agd5f's commit :

Newer asics have a lot of vram so it's less of an issue to waste a little more space for the gart page table.  This gives us some additional gart space before having to migrate to non-gart system ram for games, etc. where we use up most of vram.

http://cgit.freedesktop.org/~agd5f/linux/commit/?h=drm-next-3.12-wip&id=0daa7c6c1a55e8176e4d5a89b03bfc054a0f0266

The page tables for GART/GTT (system memory accessed via GPU's page tables) are statically allocated in VRAM -- raising the upper limit for GART allocations uses a bit more VRAM (for the tables) but can give significantly better performance when apps are using a lot of graphics memory. The memory manager can migrate buffers between VRAM, GART-accessible system memory and non-GART system memory but only the first two can be accessed by the GPU -- buffers in non-GART system memory need to be migrated back to GART before use.

[bridgman]

WTF ? 2 minute edit limit ?

Hardware from RV770 and up gets the larger allocation.