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]

Date:	13 Apr 2007 14:27:09 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Keir Fraser <keir@...source.com>
Cc:	Zachary Amsden <zach@...are.com>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...l.org>,
	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

Keir Fraser <keir@...source.com> writes:

> 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.

Unfortunately they tend to be HyperThreaded usually (except for early ones 
and Celerons) and need the LOCK anyways.

-Andi
-
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/