Date: Mon, 26 Nov 2007 09:36:25 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Stephen Montgomery-Smith <stephen@math.missouri.edu> Cc: binto <binto@triplegate.net.id>, freebsd-hackers@freebsd.org Subject: Re: Before & After Under The Giant Lock Message-ID: <20071126091342.P65286@fledge.watson.org> In-Reply-To: <20071125143546.V6583@cauchy.math.missouri.edu> References: <474830F9.90305@zirakzigil.org> <6eb82e0711240638g2cc1e54o1fb1321cafe8ff9f@mail.gmail.com> <1188.202.127.99.4.1195957922.squirrel@webmail.triplegate.net.id> <20071125110116.U63238@fledge.watson.org> <20071125143546.V6583@cauchy.math.missouri.edu>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, 25 Nov 2007, Stephen Montgomery-Smith wrote: > (Also when I run 4 threads with 2 cpus, each with hyperthreading, it goes > 2.5 to 3 times faster - surprising since hyperthreading gets quite bad press > for its performance improvements - I should add that Linux didn't do at all > well at taking advantage of hyperthreading, running at the same speed as > with 2 threads.) I've seen gradual improvements both in our ability to manage HTT and HTT itself. One of the things that gave HTT a particularly bad reputation was that it was first introduced in the P4 Xeon CPU line from Intel, and that line had extortionately expensive synchronization instructions compared to either prior or later CPU lines. As a result, even a small amount of synchronization (read: kernel locking) quickly ate any benefits of potential parallelism. More recent CPUs have managed to reduce "extionate" to "relatively expensive", which is much more manageable. Robert N M Watson Computer Laboratory University of Cambridge
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20071126091342.P65286>