Re: Fwd: 5-STABLE kernel build with icc broken
From: David Leimbach (dleimbac_at_gmail.com)
Date: 03/29/05
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Date: Tue, 29 Mar 2005 08:54:04 -0800 To: Peter Jeremy <PeterJeremy@optushome.com.au>
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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