[Bug 97260] R9 290 low performance in Linux 4.7

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97260

            Bug ID: 97260
           Summary: R9 290 low performance in Linux 4.7
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Keywords: regression
          Severity: major
          Priority: high
         Component: DRM/Radeon
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: magolobel at yahoo.com.br

Starting with Linux Kernel 4.7, the Radeon R9 290 started showing very low
performance, about 20/30% of what is available up to kernel 4.6. As can be seen
in this article, the performance regression started even before the launch of
kernel 4.7 RC1, using Alex Deucher's drm-next-4.7 branch:

http://www.phoronix.com/scan.php?page=article&item=radeon-drm-next-47&num=1

Some time later it was speculated that the problem may be with DPM:

http://www.phoronix.com/scan.php?page=news_item&px=Linux-4.7-R9-290-Regression

To replicate the bug, install Ubuntu 16.04 64bits and install kernel 4.7 from
here (preferably above rc5):

http://kernel.ubuntu.com/~kernel-ppa/mainline/ 

The performance regression will show right away. Rebooting the system and
choosing a kernel version up to 4.6 will fix the bug.

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