Date: Fri, 13 Apr 2007 20:44:25 +0200 From: Ulrich Spoerlein <uspoerlein@gmail.com> To: "Rick C. Petty" <rick-freebsd@kiwi-computer.com> Cc: freebsd-fs@FreeBSD.ORG, freebsd-current@FreeBSD.ORG Subject: Re: ZFS committed to the FreeBSD base. Message-ID: <20070413184425.GA6042@roadrunner.q.local> In-Reply-To: <20070412195947.GA96935@keira.kiwi-computer.com> References: <20070406025700.GB98545@garage.freebsd.pl> <86k5wo55s0.fsf@dwp.des.no> <20070407203411.GJ8831@cicely12.cicely.de> <86wt0n3mxv.fsf@dwp.des.no> <20070411214911.GA38351@VARK.MIT.EDU> <20070412073605.GB834@turion.vk2pj.dyndns.org> <86ps6aht1i.fsf@dwp.des.no> <20070412160603.GB92079@keira.kiwi-computer.com> <20070412185159.GB95302@nowhere> <20070412195947.GA96935@keira.kiwi-computer.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Rick C. Petty wrote: > On Thu, Apr 12, 2007 at 01:51:59PM -0500, Craig Boston wrote: > > For something this low level my opinion is it's better to stay with > > compile time options. After all, in the above example, cmpxchg8 is a > > single machine instruction. How much overhead does it add to retrieve a > > variable from memory and check it, then jump to the correct place? > > Enough that it outweighs the benefit of using that instruction in the > > first place? > > [...] > The problem is that ZFS would be compiled (by default) to work for many > platforms, and thus a majority of systems wouldn't get the nice > optimization. Disclaimer: I have no clue what cmpxchg8 actually does, but ... We are talking about optimizing a filesystem by speeding up the necessary CPU computations. Now, whenever the CPU waits for I/O (which the ZFS threads will do plenty of times) it has literally thousands of cycles to burn. I don't see how this could possibly make ZFS any faster if it does not avoid I/O operations entirely. Ulrich Spoerlein -- "The trouble with the dictionary is you have to know how the word is spelled before you can look it up to see how it is spelled." -- Will Cuppy
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20070413184425.GA6042>