Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order()

From	Afzal Mohammed <afzal.mohd.ma@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order()
Date	2015-08-22 10:00 +0200
Message-ID	<q0bSy-4j2-11@gated-at.bofh.it> (permalink)
References	(1 earlier) <pZvTj-337-3@gated-at.bofh.it> <pZwml-3AQ-11@gated-at.bofh.it> <pZOjf-4fE-1@gated-at.bofh.it> <pZPfj-5Az-3@gated-at.bofh.it> <pZPyH-6cu-23@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

Hi,

On Fri, Aug 21, 2015 at 11:01:41AM +0300, Tomi Valkeinen wrote:

> >> Possibly the patches are still good for x86 also, but that needs to be
> >> proven.
> >>
> > not exactly, because x86_64 don’t have hardware instruction to do rbit OP,
> > i compile by test :
> 
> For old drivers i386 may be more relevant than x86_64.

It seems asm bit reversal is supported in Kernel on arm & arm64 only,
not sure whether any other arch even provide asm bit reversal
instruction.

> These kind of optimizations should have some real world measurements,

Not for this case, but once measured on ARM, iirc, a 32-bit asm bit
reversal as compared to doing it in C was taking 1 cycle as opposed to
~225 cycles!, of course writing optimized C could have made it fare
better, but still would reach no-way near asm bit reversal.

Regards
Afzal
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Thread

Re: [RFC] fbdev/riva:change to use generice function to implement   reverse_order() Tomi Valkeinen <tomi.valkeinen@ti.com> - 2015-08-20 13:10 +0200
  Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order() yalin wang <yalin.wang2010@gmail.com> - 2015-08-20 13:40 +0200
    Re: [RFC] fbdev/riva:change to use generice function to implement  reverse_order() Tomi Valkeinen <tomi.valkeinen@ti.com> - 2015-08-21 08:50 +0200
      Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order() yalin wang <yalin.wang2010@gmail.com> - 2015-08-21 09:50 +0200
        Re: [RFC] fbdev/riva:change to use generice function to implement  reverse_order() Tomi Valkeinen <tomi.valkeinen@ti.com> - 2015-08-21 10:10 +0200
          Re: [RFC] fbdev/riva:change to use generice function to implement  reverse_order() Afzal Mohammed <afzal.mohd.ma@gmail.com> - 2015-08-22 10:00 +0200
            Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order() yalin wang <yalin.wang2010@gmail.com> - 2015-08-24 10:40 +0200
              Re: [RFC] fbdev/riva:change to use generice function to implement  reverse_order() Afzal Mohammed <afzal.mohd.ma@gmail.com> - 2015-08-24 15:50 +0200

csiph-web