Date: Tue, 29 Mar 2005 08:54:04 -0800 From: David Leimbach <dleimbac@gmail.com> To: Peter Jeremy <PeterJeremy@optushome.com.au> Cc: hackers@freebsd.org Subject: Re: Fwd: 5-STABLE kernel build with icc broken Message-ID: <5bbfe7d405032908542b2b0c71@mail.gmail.com> In-Reply-To: <20050329111107.GD69824@cirb503493.alcatel.com.au> References: <423C15C5.6040902@fsn.hu> <20050327133059.3d68a78c@Magellan.Leidinger.net> <20050327134044.GM78512@silverwraith.com> <20050327162839.2fafa6aa@Magellan.Leidinger.net> <5bbfe7d405032823144fc1af7b@mail.gmail.com> <5bbfe7d405032823232103d537@mail.gmail.com> <20050329111107.GD69824@cirb503493.alcatel.com.au>
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On Tue, 29 Mar 2005 21:11:07 +1000, Peter Jeremy <PeterJeremy@optushome.com.au> wrote: > On Mon, 2005-Mar-28 23:23:19 -0800, David Leimbach wrote: > >meant to send this to the list too... sorry > >> Are you implying DragonFly uses FPU/SIMD? For that matter does any kernel? > > > >I believe it does use SIMD for some of it's fast memcopy stuff for > >it's messaging system > >actually. I remember Matt saying he was working on it. > > > >http://leaf.dragonflybsd.org/mailarchive/kernel/2004-04/msg00262.html > > That's almost a year ago and specifically for the amd64. Does anyone > know what the results were? Actually I don't remember precisely what came of it, but I do remember that we had some interesting stability issues while Matt worked out some bugs around that time, I think they were related to the SIMD stuff. > > >If you can manage the alignment issues it can be a huge win. > > For message passing within the kernel, you should be able to mandate > alignment as part of the API. > > I see the bigger issue being the need to save/restore the SIMD > engine's state during a system call. Currently, this is only saved on > if a different process wants to use the SIMD engine. For MMX, the > SIMD state is the FPU state - which is non-trivial. The little > reading I've done suggests that SSE and SSE2 are even larger. > > Saving the SIMD state would be more expensive that using integer > registers for small (and probably medium-sized) copies. > Yes, you'd have to have a fairly smart copy to know when to avoid the setup overhead. Apple's bcopy stuff does a lot of checking if I recall. It's been a while since I've looked at that either. [the stuff that's mapped into the COMM_PAGE of Mac OS X 10.3.x processes] Dave > -- > Peter Jeremy >
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