linux-kernel - Re: [RFC] fbdev/riva:change to use generice function to implement reverse

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 24 Aug 2015 16:31:13 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Afzal Mohammed <afzal.mohd.ma@...il.com>
Cc:	Tomi Valkeinen <tomi.valkeinen@...com>, adaplas@...il.com,
	plagnioj@...osoft.com, linux-fbdev@...r.kernel.org,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order()


> On Aug 22, 2015, at 15:53, Afzal Mohammed <afzal.mohd.ma@...il.com> wrote:
> 
> 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.

i only submit the bit reverse patch for arm / arm64 arch,
i am not sure if there are some other arch also have hard ware bit reverse 
instructions, need arch maintainers to submit if their arch also have these hard
ware instructions . :)

> 
>> 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.
> 


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