Re: MMX bzero of a page...

David S. Miller (davem@dm.cobaltmicro.com)
Wed, 11 Mar 1998 14:39:07 -0800


Date: Wed, 11 Mar 1998 15:44:57 -0500 (EST)
From: "Benjamin C.R. LaHaise" <blah@kvack.org>

Some improvements that need to be made to the patch before it's
integrated are:

a) when saving FPU state, it should be saved to task that it
belongs to. (see the scheduler lazy-FPU saving tricks)
b) only bother saving the FPU state if the last user of the FPU
was a user process

Actually, what is easier is to store the FPU regs to the local stack
frame. We are going to do this with the Ultra VIS stuff soon, whats
nice on VIS is you can use the high bandwidth stores to stuff the FPU
registers into the save area. I don't know if MMX is like this.

c) perhaps add a fallback mechanism for machines that don't have
an FPU, or where the FPU is slow? That way the one-kernel-fits-all people
can still get the performance benefit.

Look into the btfixup mechanism the 32-bit sparc port now uses in the
vger CVS sources. You can have multiple memcpy/memset
etc. implementations, pick the one which performs best at boot time,
and make it zero cost.

Later,
David S. Miller
davem@dm.cobaltmicro.com

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