AMD R600g Still Tackling Hierarchical Z
Written by Michael Larabel in AMD on 5 June 2012 at 09:29 PM EDT. 36 Comments
While patches have been around for more than one year to support Hierarchical Z on the ATI/AMD R600 open-source driver, the Gallium3D support still hasn't been merged.

Patches have been around for over one year and while the Radeon DRM kernel driver changes have been made, the Mesa/Gallium3D changes for user-space are still missing out. Hierarchical Z, or more easily known as HiZ, is what allows to-be-rendered pixels to be checked against the z-buffer before hitting the rendering pipeline to know whether the pixel can be potentially discarded early.

HiZ has been around for ages and the support is all set for the R300g driver and has existed on the Intel driver, but the mainlining of the HiZ R600g support has been stagnant.

As the first Mesa support update in four months, Jerome Glisse put out a new version of his R600 HiZ Mesa patch as part of this BugZilla comment. Jerome's "r600g-add-htile-support-v4" does "rebase on top of lastest mesa, disable CB export when clearing htile surface to avoid wasting bandwidth" and he mentions "this one actually improve[s] performance." Sadly it's not in Mesa master but rather his own personal directory, but for those who want it, it's there. This patch amounts to about 400 lines of code and uses HTILE setup and Fast Z clear, but doesn't yet take advantage of HiS.

When speaking of not-merged-or-enabled open-source Radeon driver work, with the Linux 3.5 kernel it still doesn't enable PCI Express 2.0 support by default. PCI-E 2.0 can really boost the Radeon driver performance.

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Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter or contacted via

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