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Here's Why Radeon Graphics Are Faster On Linux 3.12

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  • Here's Why Radeon Graphics Are Faster On Linux 3.12

    Phoronix: Here's Why Radeon Graphics Are Faster On Linux 3.12

    Yesterday I published benchmarks showing the AMD Radeon graphics being much faster on Linux 3.12. Ten graphics cards were benchmarked and many of them were showing rather remarkable OpenGL frame-rate performance improvements when moving from the Linux 3.11 to Linux 3.12 Git kernel. This large comparison came after benchmarks I did this weekend on a single Radeon HD graphics card showed the Linux 3.12 kernel delivering the best performance of any recent kernel release. The only thing was, this AMD Radeon performance improvement baffled the upstream developers. The AMD developers were taken off-guard and didn't have an explanation why the Linux 3.12 kernel performance is faster... Now thanks to automated testing and bisecting by the Phoronix Test Suite, I have an answer.

    http://www.phoronix.com/vr.php?view=19208

  • #2
    so gaming above 60fps should basically be done on performance govenor..? are there other workloads that could benefit from it?

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    • #3
      It's strange that the CPU workload is not so high, but an increase in frequency changes so much the performance.

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      • #4
        So, is this really a improvement?

        It just means the open source AMD radeon driver depends too much on the cpu instead of, duh, the processing power of the graphic card.
        The other drivers are not affected because they actually use the graphic card instead of the CPU.

        Also I don't think always keeping the CPU on its limit is good either, I can imagine there is much more power wasted now since the goal for power saving is too sleep as much as possible and when in use, on a frequency as low as possible.

        Am I wrong? Maybe, but I doubt this really is the "next big thing"

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        • #5
          Originally posted by phoronix View Post
          Phoronix: Here's Why Radeon Graphics Are Faster On Linux 3.12

          Yesterday I published benchmarks showing the AMD Radeon graphics being much faster on Linux 3.12. Ten graphics cards were benchmarked and many of them were showing rather remarkable OpenGL frame-rate performance improvements when moving from the Linux 3.11 to Linux 3.12 Git kernel. This large comparison came after benchmarks I did this weekend on a single Radeon HD graphics card showed the Linux 3.12 kernel delivering the best performance of any recent kernel release. The only thing was, this AMD Radeon performance improvement baffled the upstream developers. The AMD developers were taken off-guard and didn't have an explanation why the Linux 3.12 kernel performance is faster... Now thanks to automated testing and bisecting by the Phoronix Test Suite, I have an answer.

          http://www.phoronix.com/vr.php?view=19208
          http://phoronix.com/forums/showthrea...esa-perfomance - 05-02-2013

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          • #6
            As I remember developers from Croteam discover that default ondemand governor slow down their engine in Novermber of 2012. They recommend everyone switch to performance governor before starting Serious Sam 3. Hopefully, we probably doesn't need switch to performance governor any more.
            Last edited by RussianNeuroMancer; 10-15-2013, 04:17 AM.

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            • #7
              Do these changes affect GPU's from the SI series?

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              • #8
                Nice job, this is the sort of stuff I was hoping for with per-commit benchmarking. And it's already working before it really got started! :P

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                • #9
                  Why use ondemand in the first place?

                  Why are we using ondemand for benchmarking in the first place? Benchmarking should be done to see what the system can do in terms of performance and using performance governor should be the "default" in that scenario. Does Michael use ondemand because he's interested in power consumption as well?

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                  • #10
                    Originally posted by RussianNeuroMancer View Post
                    As I remember developers from Croteam discover that default ondemand governor slow down their engine in Novermber of 2012. They recommend everyone switch to performance governor before starting Serious Sam 3. Hopefully, we probably doesn't need switch to performance governor any more.
                    Additionally, the game locks threads on cores.

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                    • #11
                      Originally posted by kwahoo View Post
                      Additionally, the game locks threads on cores.
                      Thanks for the link. So the Croteam guys have figured out the reason quite a while ago...
                      We have determined through testing that the "ondemand" governor (which is default, and which you have) seems to have some bugs and causes the erratic behavior that you see on your FPS graph. It appears as if the governor and scheduler interact in a weird way so that governor downclocks less used cores, but then the scheduler moves the main thread to that underclocked core, which the governor then clocks back, etc ad nauseam. We have contacted kernel devs, most notably developers from Intel that are working on that area, but they seem to still be looking into this.

                      The only workaround that we can come up from application side was to set strict affinity for each thread.

                      Ultimately, it is best if you switch to using the "performance" governor.

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                      • #12
                        So basically this confirms that benchmarking with games that output 300 FPS is completely a waste of time ....

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                        • #13
                          Intel CPUs are supported also by newer P-state driver with performance governor which should scale frequency like old ondemand one, but more reliably.

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                          • #14
                            Does this affect all CPUs or only some specific ones? I own a Phenom II x6.

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                            • #15
                              Originally posted by matyas View Post
                              Why are we using ondemand for benchmarking in the first place? Benchmarking should be done to see what the system can do in terms of performance and using performance governor should be the "default" in that scenario. Does Michael use ondemand because he's interested in power consumption as well?
                              I second this. People who are serious about performance should always set the "performance" governor. I even removed the file /etc/init.d/ondemand, so that I always get "performance" on boot. The init.d script sets "ondemand" after 1 minute or so after boot, i.e. when you least expect it, which messes up benchmark results. If you play games with the "ondemand" governor and complain about performance to us, you're wasting our time.

                              While it's a good thing that we know what the problem was, it's also a big fail for Phoronix. "ondemand" should never ever be used for benchmarking.

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