Subject: Re: Kernel calls - args in registers
To: Michael Smith <firstname.lastname@example.org>
From: John S. Dyson <email@example.com>
Date: 11/20/1996 00:32:38
> Travis Hassloch x231 stands accused of saying:
> > One thing I thought might make a worthwhile gain is to make all
> > intrakernel calls use registers -- and if possible, all kernel calls.
> I think Bruce will have opinions here, but IMHO using registers for
> arg passing isn't much of a win, especially on the x86 where there
> are so few of them.
I have an opinion also... I have already recompiled much of the FreeBSD kernel
to use the register passing convention. Not really worth it. F.E.
our approx 500-530usec fork perf (on a P5-166) doesn't budge almost
at all with a change in calling convention... The pgcc compiler or
-fomit-frame-pointer makes much more difference (if it works to compile
your kernel :-) -- sometimes "advanced options" don't work to compile
ours...) (BTW, even that difference is in the 5% or so range.)
I think that algorithmic improvements in the kernel are where "it is."
It is likely that if we use the register passing conventions in the
kernel -- it'll be because there is a worthwhile improvement. I haven't
seen a significant one -- YET. If you see one -- let me know!!!