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Subject: Re: [PATCH] I3 sched tweaks...
From: Justin Carlson <justincarlson@cmu.edu>
To: Robert Love <rml@tech9.net>
Cc: mingo@elte.hu, Rusty Russell <rusty@rustcorp.com.au>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, 2002-01-16 at 16:10, Robert Love wrote:
> On Wed, 2002-01-16 at 17:46, Ingo Molnar wrote:
>=20
> > we pass pointers across functions regularly, even if the pointer could =
be
> > calculated within the function. We do this in the timer code too. It's
> > slightly cheaper to pass an already existing (calculated) 'current'
> > pointer over to another function, instead of calculating it once more i=
n
> > that function. This will be especially true once we make 'current' a ti=
ny
> > bit more expensive (Alan's kernel stack coloring rewrite will do that i
> > think, it will be one more instruction to get 'current'.)
>=20
> Maybe we should benchmark it?  It is very easy to calculate current.
>=20
> Certainly I see the benefit if we start coloring the pointer (it adds 2
> instructions I believe) but let's make sure it is worth passing another
> 32-bit argument.  It could very well be, schedule_tick is called
> enough...

Don't forget that, in non-x86 land, current tends to be just kept in a=20
register.  No computations required.  Certainly passing it around on,
e.g. mips is a clear loss.

-Justin


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