linux-kernel - Re: [PATCH RFC] [X86] performance improvement for memcpy

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 for Android: free password hash cracker in your pocket

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

Date:	Fri, 13 Nov 2009 00:04:54 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Pavel Machek <pavel@....cz>, "Ma, Ling" <ling.ma@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by
 fast string.

On 11/12/2009 11:33 PM, Ingo Molnar wrote:
> 
> * Pavel Machek <pavel@....cz> wrote:
> 
>>> Ling, if you are interested, could you send a user-space test-app to 
>>> this thread that everyone could just compile and run on various older 
>>> boxes, to gather a performance profile of hand-coded versus string ops 
>>> performance?
>>>
>>> ( And i think we can make a judgement based on cache-hot performance
>>>   alone - if then the strings ops will perform comparatively better in
>>>   cache-cold scenarios, so the cache-hot numbers would be a conservative
>>>   estimate. )
>>
>> Ugh, really? I'd expect cache-cold performance to be not helped at all 
>> (memory bandwidth limit) and you'll get slow down from additional 
>> i-cache misses...
> 
> That's my point - the new code is shorter, which will run comparatively 
> faster in a cache-cold environment.
> 

memcpy_c by itself is by far the shortest variant, of course.

The question is if it makes sense to use the long variants for short (<
1024 bytes) copies.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

--
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/