Date: Fri, 13 Apr 2007 16:52:45 +0200 (CEST) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-current@FreeBSD.ORG, bde@zeta.org.au, des@des.no, freebsd-fs@FreeBSD.ORG, craig@xfoil.gank.org, rick-freebsd@kiwi-computer.com Subject: Re: ZFS committed to the FreeBSD base. Message-ID: <200704131452.l3DEqjXv040099@lurza.secnetix.de> In-Reply-To: <freebsd-current.20070413164840.V31079@besplex.bde.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Bruce Evans wrote: > Not for cmpxchg8b, at least. It is a remarkably slow instruction. On > AthlonXP's it has an execution latency of 39 cycles. cmpxchg only has an > cmpxchg only has an execution latency of 6 cycles (both without a lock > prefix). I don't know how to avoid using cmpxchg8b short of using a > mutex lock/unlock pair and slightly different semantics, or a generation > count and very different semantics, but without lock prefixes the > mutex pair would be much faster than the cmpxchg8b. Using cmpxchg8b with a lock prefix wouldn't be a good idea anyway. If I remember correctly, the lock cmpxchg8b combination was the cause of the infamous "F00F" bug of old Pentium processors. It causes them to freeze. (FreeBSD has a hack to work around the problem, as you certainly know ... I don't know exactly how it works.) Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M. Handelsregister: Registergericht Muenchen, HRA 74606, Geschäftsfuehrung: secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün- chen, HRB 125758, Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart FreeBSD-Dienstleistungen, -Produkte und mehr: http://www.secnetix.de/bsd It's trivial to make fun of Microsoft products, but it takes a real man to make them work, and a God to make them do anything useful.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200704131452.l3DEqjXv040099>