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

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Message-ID: <1542040904.2661.35.camel@suse.de>
Date:   Mon, 12 Nov 2018 17:41:44 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     David Airlie <airlied@...hat.com>, christian.koenig@....com,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Performance regression in ast drm driver

On Mon, 2018-11-12 at 15:45 +0100, Takashi Iwai wrote:
> On Mon, 12 Nov 2018 15:36:07 +0100,
> Jean Delvare wrote:
> > Takashi asked me to compare the contents of
> > /sys/kernel/debug/x86/pat_memtype_list before and after the commit
> > above. Before the commit, we have:
> > 
> > uncached-minus @ 0xfafe0000-0xfb000000
> > uncached-minus @ 0xfb000000-0xfb005000
> > write-combining @ 0xfb005000-0xfb584000
> > 
> > After the commit, we have:
> > 
> > uncached-minus @ 0xfafe0000-0xfb000000
> > uncached-minus @ 0xfb000000-0xfb005000
> > uncached-minus @ 0xfb000000-0xfb800000
> > uncached-minus @ 0xfb005000-0xfb584000
> 
> Just to be sure:
> could you double-check whether you're checking the right order
> (i.e. not checking against the revert)?  The change above looks
> illogical from what I can see from the commit...

Yes, I double checked and can only confirm what I wrote above. However
while checking I noticed another strange thing: the contents of
pat_memtype_list depend on whether I'm reading the file from an xterm
or from the text console (Ctrl+Alt+F2). So I summarize again:

Commit "drm/drivers: add support for using the arch wc mapping API"
APPLIED, reading pat_memtype_list from the text console:

uncached-minus @ 0xfafe0000-0xfb000000
uncached-minus @ 0xfb000000-0xfb005000
uncached-minus @ 0xfb000000-0xfb800000
uncached-minus @ 0xfb005000-0xfb584000

Commit "drm/drivers: add support for using the arch wc mapping API"
APPLIED, reading pat_memtype_list from an xterm:

uncached-minus @ 0xfafe0000-0xfb000000
uncached-minus @ 0xfb000000-0xfb005000
uncached-minus @ 0xfb000000-0xfb800000

Commit "drm/drivers: add support for using the arch wc mapping API"
REVERTED, reading pat_memtype_list from the text console:

uncached-minus @ 0xfafe0000-0xfb000000
uncached-minus @ 0xfb000000-0xfb005000
write-combining @ 0xfb005000-0xfb584000

Commit "drm/drivers: add support for using the arch wc mapping API"
REVERTED, reading pat_memtype_list from an xterm:

uncached-minus @ 0xfafe0000-0xfb000000
uncached-minus @ 0xfb000000-0xfb005000

If you don't find it logical, remember that if things were the way they
are supposed to be, customers and myself would not be reporting this
bug ;-)

-- 
Jean Delvare
SUSE L3 Support