[Bug 105038] slight lags in youtube video 1080p since a change in kernel 4.15 related to drm/ttm

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105038

            Bug ID: 105038
           Summary: slight lags in youtube video 1080p since a change in
                    kernel 4.15 related to drm/ttm
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: mister.freeman at laposte.net

Created attachment 137264
  --> https://bugs.freedesktop.org/attachment.cgi?id=137264&action=edit
dmesg

Hello,

I have a radeon HD4650 pcie, I use the radeon driver,

since a new algorithm for drm/ttm introduced in kernel 4.15.x then I notice a
performance loss in video playback, especially when the format is 1080p ( for
example youtube video ), some lags are visible ( for example travelling images,
vertical scroll of the credits in a video ),

the bug has been introduced since this commit :

commit 648bc3574716400acc06f99915815f80d9563783
Author: Christian König <christian.koenig at amd.com>
Date:   Thu Jul 6 09:59:43 2017 +0200

    drm/ttm: add transparent huge page support for DMA allocations v2

    Try to allocate huge pages when it makes sense.

    v2: fix comment and use ifdef

    Signed-off-by: Christian König <christian.koenig at amd.com>
    Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>
    Signed-off-by: Alex Deucher <alexander.deucher at amd.com>

reverting this patch solves the bug,

I have created a bug report in kernel's bugzilla :
https://bugzilla.kernel.org/show_bug.cgi?id=198511

Christian König advices me to open a bug report here for drm/radeon,

I have filmed my screen in order to demonstrate the effect of this bug, you can
see my video here :

https://www.youtube.com/watch?v=YqtleU5YBlA

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