1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking.org

Here's Why Radeon Graphics Are Faster On Linux 3.12

Michael Larabel

Published on 15 October 2013
Written by Michael Larabel
Page 2 of 5 - 108 Comments

As at least one or two readers within the Phoronix Forums had speculated, the apparent cause of the Radeon GPU performance increase comes down to a CPUfreq change. The reason for the GPU performance change appears to be this Git commit.

cpufreq: ondemand: Change the calculation of target frequency

The ondemand governor calculates load in terms of frequency and increases it only if load_freq is greater than up_threshold multiplied by the current or average frequency. This appears to produce oscillations of frequency between min and max because, for example, a relatively small load can easily saturate minimum frequency and lead the CPU to the max. Then, it will decrease back to the min due to small load_freq.

Change the calculation method of load and target frequency on the basis of the following two observations:

- Load computation should not depend on the current or average measured frequency. For example, absolute load of 80% at 100MHz is not necessarily equivalent to 8% at 1000MHz in the next sampling interval.

- It should be possible to increase the target frequency to any
value present in the frequency table proportional to the absolute load, rather than to the max only, so that:

Target frequency = C * load where we take C = policy->cpuinfo.max_freq / 100.

Tested on Intel i7-3770 CPU @ 3.40GHz and on Quad core 1500MHz Krait. Phoronix benchmark of Linux Kernel Compilation 3.1 test shows an increase ~1.5% in performance. cpufreq_stats (time_in_state) shows that middle frequencies are used more, with this patch. Highest and lowest frequencies were used less by ~9%.

[rjw: We have run multiple other tests on kernels with this change applied and in the vast majority of cases it turns out that the resulting performance improvement also leads to reduced consumption of energy. The change is additionally justified by the overall simplification of the code in question.]

The Git commit changed cpufreq with the ondemand governor for how load is calculated. The changes were for load computation not to depend upon the current or average measured frequency and to let the governor select any target frequency proportional to the load rather than just using the max frequency. Interestingly, the developer behind this commit, Stratos Karafotis, had even used the Phoronix Test Suite for verifying the performance changes when working on the patch. However, in his testing he was using the build-linux-kernel test profile and there he found only a 1.5% performance difference. There was no mention of graphics testing having occurred during this work. The patch also mentions there may be power consumption benefits too.

It's somewhat interesting that the Radeon performance changes were due to the CPUfreq ondemand governor changes and that for the other Phoronix.com testing of the Linux 3.12 kernel so far hasn't revealed anything else too exciting: besides some file-system performance changes, the Ivy Bridge and Haswell graphics performance has been the same and in the CPU-bound tests we haven't found anything to get excited about. I haven't yet done any Nouveau Linux 3.12 kernel comparison but that testing is now warranted and will be delivering results on Phoronix shortly. With this being a non-Radeon specific change, the AMD Catalyst (and NVIDIA) drivers could also benefit from this CPU governor change, but on my testing platter is now to run some new open vs. closed-source driver benchmarks in this configuration.

Latest Linux Hardware Reviews
  1. A Walkthrough Of The New 32 System Open-Source Linux Benchmarking Test Farm
  2. Habey MITX-6771: Mini-ITX Board With Quad-Core J1900 Bay Trail
  3. OCZ Vector 150 SSD On Linux
  4. Noctua i4 CPU Cooler: Great For Cooling High-End LGA-2011v3 CPUs
Latest Linux Articles
  1. 17-Way Linux Graphics Card Comparison With Civilization Beyond Earth
  2. AMD Kaveri: Open-Source Radeon Gallium3D vs. Catalyst 14.12 Omega Driver
  3. 12-Way AMD Catalyst 14.12 vs. NVIDIA 346 Series Linux GPU Comparison
  4. AMD Catalyst 14.12 Omega Driver Brings Mixed Results For Linux Users
Latest Linux News
  1. LDC 0.15.1 Released For A D Compiler In LLVM
  2. Fedora Doesn't Yet Enable F2FS File-System Support
  3. XZ 5.2 Adds New Multi-Threaded Options
  4. Intel 2.99.917 X.Org Driver Released, 3.0 Release Finally Near
  5. Server-Side XCB Is Being Discussed For The X.Org Server
  6. Adreno A4xx Rendering With Freedreno Takes Shape
  7. Linux 3.19-rc1 Kernel Released Ahead Of Schedule
  8. X.Org Server 1.16.3 Released To Fix Security Issues
  9. Linux 3.19 Merge Window Closes Ahead Of Schedule
  10. MIPS R6 Architecture Now Supported By GCC
Latest Forum Discussions
  1. Maker3D - create your 3D RPG
  2. FPS capped on Linux (AMD fglrx drivers)
  3. Looking for an nVidia GPU, but not sure how well they are supported.
  4. Need some hand holding with upgrading xserver
  5. Speeding up systemd networking service
  6. Major Performance Breakthrough Discovered For Intel's Mesa Driver
  7. Are there an app using HSA ?
  8. The New SuperTuxKart Looks Better, But Can Cause GPU/Driver Problems