Messages in this thread |  | | Date | Thu, 9 Apr 2015 14:21:43 +0300 | From | Tomi Valkeinen <> | Subject | Re: simple framebuffer slower by factor of 20, on socfpga (arm) platform |
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On 09/04/15 14:06, Pavel Machek wrote: > On Tue 2015-04-07 14:19:33, Geert Uytterhoeven wrote: >> Hi Pavel, >> >> On Tue, Apr 7, 2015 at 2:12 PM, Pavel Machek <pavel@ucw.cz> wrote: >>> 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.
Interesting. I can reproduce this also on TI's AM437x board, on 3.14 kernel. Without the patch:
# time cat /dev/fb0 > /dev/null real 0m 0.01s user 0m 0.00s sys 0m 0.01s
With the patch:
# time cat /dev/fb0 > /dev/null real 0m 0.19s user 0m 0.01s sys 0m 0.17s
> Archit do you know what is going on there? Should the revert be filled > for 4.0?
(Cc'ing Archit's new email)
> > Pavel > > commit 981409b25e2a99409b26daa67293ca1cfd5ea0a0 > Author: Archit Taneja <archit@ti.com> > 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 <archit@ti.com> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com> > Cc: H Hartley Sweeten <hsweeten at visionengravers.com> > Cc: Alexander Shiyan <shc_work@mail.ru> > Cc: Russell King <linux@arm.linux.org.uk>
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