linux-kernel - Re: simple framebuffer slower by factor of 20, on socfpga (arm) platform

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Date:	Tue, 7 Apr 2015 16:24:45 +0200
From:	Marek Vasut <marex@...x.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	Dinh Nguyen <dinh.linux@...il.com>,
	"Jean-Christophe PLAGNIOL-VILLARD" <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Rob Clark <robdclark@...il.com>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: simple framebuffer slower by factor of 20, on socfpga (arm) platform

On Tuesday, April 07, 2015 at 02:19:33 PM, Geert Uytterhoeven wrote:
> Hi Pavel,
> 
> On Tue, Apr 7, 2015 at 2:12 PM, Pavel Machek <pavel@....cz> wrote:
> > I have an socfpga board, which uses has simple framebuffer implemented
> > in the FPGA. On 3.15, framebuffer is fast:
> > 
> > root@...abuibui:~# time cat /dev/fb0 > /dev/null
> > real               0m 0.00s
> > user               0m 0.00s
> > sys                0m 0.00s
> > 
> > on 3.18, this takes 220msec. Similar slowdown exists for
> > writes. Simple framebuffer did not change at all between 3.15 and
> > 3.18; resource flags of the framebuffer are still same (0x200).
> > 
> > If I enable caching on 3.18, it speeds up a bit, to 70msec or
> > so... Which means problem is not only in caching.
> > 
> > Any ideas?
> 
> My first guess was  commit 67dc0d4758e5 ("vt_buffer: drop console buffer
> copying optimisations"), but this was introduced only in v4.0-rc1.
> 
> Just in case you encounter another performance regression after upgrading
> to a more modern kernel ;-)

Why don't you use the Altera VIP FB on SoCFPGA ?

Best regards,
Marek Vasut
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