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

On Tue 2015-04-07 14:19:33, Geert Uytterhoeven wrote:

Hi Pavel,

On Tue, Apr 7, 2015 at 2:12 PM, Pavel Machek [off-list ref] wrote:

quoted

I have an socfpga board, which uses has simple framebuffer implemented
in the FPGA. On 3.15, framebuffer is fast:

root@wagabuibui:~# 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 ;-)

:-). I did a git bisect, and it pointed to this. And reverting it
indeed fixes the problem in 3.18. Problem is still there in 4.0.

Archit do you know what is going on there? Should the revert be filled
for 4.0?

								Pavel

commit 981409b25e2a99409b26daa67293ca1cfd5ea0a0
Author: Archit Taneja [off-list ref]
Date:   Fri Nov 16 14:46:04 2012 +0530

    fbdev: arm has __raw I/O accessors, use them in fb.h

    This removes the sparse warnings on arm platforms:

    warning: cast removes address space of expression

 Signed-off-by: Archit Taneja [off-list ref]
 Signed-off-by: Tomi Valkeinen [off-list ref]
 Cc: H Hartley Sweeten <hsweeten at visionengravers.com>
 Cc: Alexander Shiyan [off-list ref]
 Cc: Russell King [off-list ref]

Gr{oetje,eeting}s,

                        Geert

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

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