linux-kernel - Re: [PATCH v3 0/7] GPU workload hints for better performance

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Date:   Wed, 30 Aug 2023 17:19:17 +0200
From:   Michel Dänzer <michel.daenzer@...lbox.org>
To:     "Lazar, Lijo" <Lijo.Lazar@....com>,
        "Yadav, Arvind" <Arvind.Yadav@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Sharma, Shashank" <Shashank.Sharma@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        "airlied@...il.com" <airlied@...il.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "Kuehling, Felix" <Felix.Kuehling@....com>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/7] GPU workload hints for better performance

On 8/28/23 17:02, Lazar, Lijo wrote:
> [AMD Official Use Only - General]
> 
> 
> As mentioned with an older version of this series, this is an 'abuse' of power profile interface.
> 
> This series is oversimplifying what PMFW algorithms are supposed to be doing. Whatever this series is doing, FW can do it better.
> 
> To explain in simpler terms - it just tries to boost a profile based on ring type without even knowing how much of activity a job can trigger on a particular ring. A job scheduled to a GFX ring doesn't deserve a profile boost unless it can create a certain level of activity. In CPU terms, a job scheduled to a processor doesn't mean it deserves a frequency boost of that CPU.  At minimum it depends on more details like whether that job is compute bound or memory bound or memory bound. 
> 
> While FW algorithms are designed to do that, this series tries to trivialise all such things.
> 
> Unless you are able to show the tangible benefits in some terms like performance, power, or performance per watt,  I don't think this should be the default behaviour where driver tries to override FW just based on job submissions to rings.

I know at least one tangible benefit this would have: a snappier GNOME desktop with lower input → output latency on many laptops. The bootup default profile doesn't work well for that IME.

It should also help for issues like
https://gitlab.freedesktop.org/drm/amd/-/issues/1500 .

That said, I agree this approach is very aggressive. I think it might be acceptable with AC power, not sure about on battery though. (There might be better performance/power profile mechanisms to hook into than AC vs battery)


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer