Date: Tue, 29 Mar 2005 22:57:28 -0500 From: jason henson <jason@ec.rr.com> To: Peter Jeremy <PeterJeremy@optushome.com.au> Cc: hackers@freebsd.org Subject: Re: Fwd: 5-STABLE kernel build with icc broken Message-ID: <424A23A8.5040109@ec.rr.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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Peter Jeremy 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? > > > >>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. > > > Later in that thread they discuss skipping the restore state to make things faster. The minimum buffer size they say this will be good for is between 2-4k. Does this make sense, or am I showing my ignorance? http://leaf.dragonflybsd.org/mailarchive/kernel/2004-04/msg00264.html
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