From: Afzal Mohammed <afzal.mohd.ma@gmail.com>
To: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: yalin wang <yalin.wang2010@gmail.com>,
adaplas@gmail.com, plagnioj@jcrosoft.com,
linux-fbdev@vger.kernel.org,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order()
Date: Sat, 22 Aug 2015 07:53:34 +0000 [thread overview]
Message-ID: <20150822075310.GA2337@afzalpc> (raw)
In-Reply-To: <55D6DAE5.20304@ti.com>
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
WARNING: multiple messages have this Message-ID (diff)
From: Afzal Mohammed <afzal.mohd.ma@gmail.com>
To: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: yalin wang <yalin.wang2010@gmail.com>,
adaplas@gmail.com, plagnioj@jcrosoft.com,
linux-fbdev@vger.kernel.org,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order()
Date: Sat, 22 Aug 2015 13:23:10 +0530 [thread overview]
Message-ID: <20150822075310.GA2337@afzalpc> (raw)
In-Reply-To: <55D6DAE5.20304@ti.com>
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
next prev parent reply other threads:[~2015-08-22 7:53 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-10 10:12 [RFC] fbdev/riva:change to use generice function to implement reverse_order() yalin wang
2015-08-10 10:12 ` yalin wang
2015-08-20 11:02 ` Tomi Valkeinen
2015-08-20 11:02 ` Tomi Valkeinen
2015-08-20 11:30 ` yalin wang
2015-08-20 11:30 ` yalin wang
2015-08-21 6:41 ` Tomi Valkeinen
2015-08-21 6:41 ` Tomi Valkeinen
2015-08-21 7:46 ` yalin wang
2015-08-21 7:46 ` yalin wang
2015-08-21 8:01 ` Tomi Valkeinen
2015-08-21 8:01 ` Tomi Valkeinen
2015-08-22 7:53 ` Afzal Mohammed [this message]
2015-08-22 7:53 ` Afzal Mohammed
2015-08-24 8:31 ` yalin wang
2015-08-24 8:31 ` yalin wang
2015-08-24 13:41 ` Afzal Mohammed
2015-08-24 13:53 ` Afzal Mohammed
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