Here's Why Radeon Graphics Are Faster On Linux 3.12
Once finding the root cause of the problem, I took it one step further to better welcome and thank the new Phoronix Premium subscribers and those who contributed yesterday for the Radeon testing. The Phoronix Test Suite also has a built-in system-monitoring module to be able to simultaneously monitor various hardware and software sensors as benchmarks are taking place... The supported sensors range from the CPU temperature to disk write speeds to network sensors, but also the real-time CPU frequency and CPU usage. Taking advantage of the support in this case just requires setting MONITOR=cpu.freq,cpu.usage as an environment variable prior to running any Phoronix Test Suite benchmarks (to see all available sensors, run phoronix-test-suite system-sensors; note on Ubuntu 13.10 they removed PHP5 PCNTL support unexpectedly so you may need to rebuild PHP manually for the multi-threaded system sensor monitoring support).
In having the Phoronix Test Suite monitor the CPU frequency and usage in real-time while the different OpenGL benchmarks were happening, we were able to get a better idea for how the CPUfreq ondemand governor is behaving differently between the Linux 3.11 and Linux 3.12 Git kernels. Testing was done on an Intel Core i7 4770K "Haswell" system and the graphics card for this system monitoring session was the AMD Radeon HD 6950. System details, logs, and other information can be found within 1310143-SO-LINUX312R98.
For OpenArena 0.8.8 between 3.11 and 3.12 Git, the Radeon HD 6950 on the open-source driver with Mesa 10.0-devel R600 Gallium3D was 14% faster by just upgrading the kernel.
The Phoronix Test Suite's system monitor module was polling the CPU frequency once per second and it's clearly showing a difference between the Linux 3.11 and 3.12 kernels. With the Linux 3.11 kernel, this CPU-limited game was staying mostly at its lowest 800MHz stepping most of the time and quite often then bumping up to 3.5GHz. With the Linux 3.12 kernel for the entire duration of the testing the CPU frequency was just going between its 3.5GHz highest base frequency and 3.9GHz Turbo frequency and never dropping down to its lowest 800MHz state. When running the game, the CPU governor isn't letting the CPU slowdown. This is good for performance and we'll see in some benchmarks shortly how this impacts the power consumption while gaming on Linux.
The CPU frequency staying in its highest states during all of the OpenArena testing, the average CPU frequency as a percent was then lower with the Linux 3.12 kernel.
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