Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

From: Tommaso Cucinotta
Date: Mon Apr 23 2012 - 19:21:23 EST

Il 23/04/2012 22:58, Peter Zijlstra ha scritto:
On Mon, 2012-04-23 at 22:55 +0100, Tommaso Cucinotta wrote:
why not write this straight in asm, i.e., multiply 64*64 then divide by
64 keeping the intermediate result on 128 bits?
If you know of a way to do this for all 30 odd architectures supported
by our beloved kernel, do let me know ;-)

Yes I can do it for x86_64, but people tend to get mighty upset if you
break the compile for all other arches...

rather than breaking compile, I was thinking more of using the optimization for a more accurate comparison on archs that have 64-bit mul and 128-bit cmp, and leaving the overflow on other archs. Though, that would imply a difference in behavior on those borderline cases (very big periods I guess).

However, I'm also puzzled from what would happen by compiling the current code on mostly 16-bit micros which have very limited 32-bit operations...


Tommaso Cucinotta, Computer Engineering PhD, Researcher
ReTiS Lab, Scuola Superiore Sant'Anna, Pisa, Italy
Tel +39 050 882 024, Fax +39 050 882 003

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