linux-kernel - Re: [PATCH 0/4] i386 - pte update optimizations

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: <C2450C95.D3F6%keir@xensource.com>
Date:	Fri, 13 Apr 2007 10:31:49 +0100
From:	Keir Fraser <keir@...source.com>
To:	Zachary Amsden <zach@...are.com>, "H. Peter Anvin" <hpa@...or.com>
CC:	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@....de>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Chris Wright <chrisw@...s-sol.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hugh@...itas.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] i386 - pte update optimizations

On 13/4/07 03:24, "Zachary Amsden" <zach@...are.com> wrote:

>> You do know that P6 and higher don't do locked bus references as long
>> as the value is in the cache, right?
> 
> Yes.  Even then, last time I clocked instructions, xchg was still slower
> than read / write, although I could be misremembering.  And it's not
> totally clear that they will always be in cached state, however, and for
> SMP, we still want to drop the implicit lock in cases where the
> processor might not know they are cached exclusive, but we know there
> are no other racing users.  And there are plenty of old processors out
> there to still make it worthwhile.

LOCKed instruction suck really badly on the netburst microarchitecture (like
factor of 10x, or not far off). I think it's probably because of their side
effect of serialising memory accesses, causing horrible pipeline stalls.

 -- Keir

-
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/