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

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

Message-ID: <8FED46E8A9CA574792FC7AACAC38FE7714FEB070EE@PDSMSX501.ccr.corp.intel.com>
Date:	Fri, 13 Nov 2009 13:33:21 +0800
From:	"Ma, Ling" <ling.ma@...el.com>
To:	Pavel Machek <pavel@....cz>
CC:	"H. Peter Anvin" <hpa@...or.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC] [X86] performance improvement for memcpy_64.S by
	fast string.

>Well, so you are running cache hot and it is only a win on huge
>copies... how common are those?
>
Hi Pavel Machek
Yes, we intend to introduce movsq for huge hot size(over 1024bytes)
and avoid regression for less 1024bytes. I guess you suggest using
prefetch instruction for cold data (if I was wrong please correct me).
memcpy don't know whether data has been in cache or not,
so only when copy size is over (first level 1 cache)/2 and lower
(last level cache)/2 , prefetch will get benefit. Currently first
level cache size of most cpus is around 32KB, so it is useful for prefetch 
when copy size is over 16KB, but as H. Peter Anvin mentioned in last email,
over 16KB copy in kernel is rare.

Thanks
Ling   

--
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/