linux-kernel - Re: Performance regression in ast drm driver

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Message-ID: <20181110093918.52ec9f0f@endymion>
Date:   Sat, 10 Nov 2018 09:39:18 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     David Airlie <airlied@...hat.com>
Cc:     christian.koenig@....com, "Iwai, Takashi" <tiwai@...e.de>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Performance regression in ast drm driver

On Fri, 9 Nov 2018 10:04:03 +1000, David Airlie wrote:
> This seems likely to be a hw problem with PCI writes to the AST "GPU",
> since it's just some sort of RAM + ARM on the end of a PCIE bus, we've
> definitely seen possible issues in the past with write combining
> around some of the mga GPUs with some CPUs.
> 
> Have we seen the problem across a number of AST devices?

The reports I received from customers were all on AST 2500 devices (on
Supermicro X11DPi-N, Supermicro X11DPH-T and Asus WS C621 Sage).

I was able to reproduce "the problem" on my old Asus Z6NA-D6 which has
either an AST 2050 device if I trust the board specifications on
asus.com, or an AST 1100 if I trust /var/log/Xorg.0.log.

Note however that I am still not certain that the problem I am seeing
is the same as what both customers reported. It is possible that we
have 2 different issues.

-- 
Jean Delvare
SUSE L3 Support