70 Intel DRM Linux Kernel Patches Bring Some Performance Optimizations

Chris Wilson of Intel's Open-Source Technology Center hasn't yet managed the xf86-video-intel 3.0 DDX release, but over in kernel-space, he's just published a set of 70 new DRM patches for the Intel kernel driver.

This patch series contains some "low-hanging fruit" for the Intel DRM driver that improve micro-benchmarks and other items while affecting several generations of Intel HD/Iris Graphics support.

A few of the 70 patches in particular stand out for users:

- Aggressive down-clocking for Bay Trail. Using the same strategy as Sandy Bridge and Ivy Bridge, Bay Trail hardware should now re-clock up and down quicker.

- "Boost GPU frequency if we detect outstanding pageflips." If there's page-flips queued but not yet processed when hitting a vblank, the Intel DRM driver will ensure the GPU is running at its top speed in order to try to get done the remaining work.

- Optimistically spinning for request completion. Chris noted, "In the most favourable of microbenchmarks, this can increase performance by around 15% - though in practice improvements will be marginal and rarely noticeable."

- Eliminating vmap overhead in the command parser. According to Wilson's Ivy Bridge results, there's performance improvements to see in some micro tests like x11perf and glxgears.

- Cache the last command descriptor when parsing. This too can benefit some micro-benchmarks.

As Intel's basically done with new work for Linux 4.1 when it comes to their graphics driver, these 70 patches are likely material to show up for the Linux 4.2 kernel in the summer.