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

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Date:	Fri, 24 Apr 2015 15:46:56 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	Pavel Machek <pavel@....cz>,
	Archit Taneja <architt@...eaurora.org>,
	Marek Vasut <marek.vasut@...il.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	Dinh Nguyen <dinh.linux@...il.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.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>,
	Alexander Shiyan <shc_work@...l.ru>,
	Russell King <linux@....linux.org.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>
Subject: Re: simple framebuffer slower by factor of 20, on socfpga (arm) platform

On Fri, Apr 24, 2015 at 3:40 PM, Tomi Valkeinen <tomi.valkeinen@...com> wrote:
> On 24/04/15 16:29, Pavel Machek wrote:
>> On Fri 2015-04-10 12:35:52, Archit Taneja wrote:
>>>> That said, if the fb is in RAM, and is only written by the CPU, I think
>>>> a normal memcpy() for fb_memcpy_fromfb() should be fine...
>>>
>>> I didn't test for performance regressions when I posted this patch.
>>>
>>> A look at _memcpy_fromio in arch/arm/kernel/io.c shows that readb() is used
>>> all the time, even when the source and destination addresses are aligned for
>>> larger reads to be possible. Other archs seem to use readl() or readq() when
>>> they can. Maybe that makes memcpy_fromio slower than the implementation of
>>> memcpy on arm?
>>
>> Ok, can you prepare a patch for me to try? Or should we just revert
>> the original commit?
>
> The old way worked fine, afaik, so maybe we can revert. But still, isn't
> it more correct to use memcpy_fromio? It's (possibly) io memory we have
> here.

Yes it is.

So please optimize ARM's _memcpy_fromio(), _memcpy_toio(), and _memset_io().
That will benefit other drivers on ARM, too.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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