[PATCH 20/23] drm/amd/display: Disables dynamic memory clock switching in games

[Vanzylldejong, Harry]

[AMD Official Use Only - General]

Hi Chandan,

When using Firmware Assisted Memory clock Switching (FAMS), when the memory clock is switched the frame rate is dropped for at least 1 frame,
sometimes 2-3 frames to make the V-Blank long enough to handle the period where the GDDR6 memory is unavailable when the memory clock switches.
This drop may be noticeable by gamers, especially if the memory clock wants to change it's clock rate several times a second,
which is what we observed just on the desktop.
To guarantee best game performance, we disable FAMS during game play.

Harry


-----Original Message-----
From: VURDIGERENATARAJ, CHANDAN <CHANDAN.VURDIGERENATARAJ at amd.com>
Sent: June 13, 2022 8:42 AM
To: Michel Dänzer <michel.daenzer at mailbox.org>; Mahfooz, Hamza <Hamza.Mahfooz at amd.com>; amd-gfx at lists.freedesktop.org
Cc: Wang, Chao-kai (Stylon) <Stylon.Wang at amd.com>; Liu, HaoPing (Alan) <HaoPing.Liu at amd.com>; Li, Sun peng (Leo) <Sunpeng.Li at amd.com>; Lakha, Bhawanpreet <Bhawanpreet.Lakha at amd.com>; Zhuo, Qingqing (Lillian) <Qingqing.Zhuo at amd.com>; Siqueira, Rodrigo <Rodrigo.Siqueira at amd.com>; Li, Roman <Roman.Li at amd.com>; Chiu, Solomon <Solomon.Chiu at amd.com>; Zuo, Jerry <Jerry.Zuo at amd.com>; Pillai, Aurabindo <Aurabindo.Pillai at amd.com>; Vanzylldejong, Harry <Harry.Vanzylldejong at amd.com>; Lin, Wayne <Wayne.Lin at amd.com>; Wentland, Harry <Harry.Wentland at amd.com>; Gutierrez, Agustin <Agustin.Gutierrez at amd.com>; Kotarac, Pavle <Pavle.Kotarac at amd.com>
Subject: RE: [PATCH 20/23] drm/amd/display: Disables dynamic memory clock switching in games

Hi,

Can you please elaborate on why dynamic memory clock switching can affect Game performance?

BR,
Chandan V N


>On 2022-06-10 22:52, Hamza Mahfooz wrote:
>> From: Harry VanZyllDeJong <harry.vanzylldejong at amd.com>
>>
>> [WHY]
>> Game performace may be affected if dynamic memory clock switching is
>> enabled while playing games.
>>
>> [HOW]
>> Propagate the vrr active state to dirty bit so that on mode set it
>> disables dynamic memory clock switching.
>
>So dynamic memory clock switching will be disabled whenever VRR is enabled?
>
>Note that there is ongoing discussion about how Wayland compositors could usefully keep VRR enabled all the time, as opposed to only while >there's a fullscreen application like a game. So "VRR is enabled" likely won't be equivalent to "game is running" in the long term.
>
>
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