From: "Grover, Andrew" <andrew.grover@intel.com>
To: linux-kernel@vger.kernel.org
Subject: RE: lilo vs other OS bootloaders was: FreeBSD makes progress
Date: Wed, 5 Sep 2001 14:18:51 -0700 [thread overview]
Message-ID: <4148FEAAD879D311AC5700A0C969E89006CDE0ED@orsmsx35.jf.intel.com> (raw)
> From: Helge Hafting [mailto:helgehaf@idb.hist.no]
> > I'm not advocating anything similar for Linux, I'm just
> saying it's an
> > interesting thought experiment - what if the SMP-ness of a
> machine was
> > abstracted from the kernel proper? How much of the kernel
> really cares, or
> > really *should* care about SMP/UP?
> You would also get rid of performance. The agnostic kernel would be
> slower than simply running the SMP kernel on UP.
>
> Here's why:
> You can easily make an "agnostic kernel & modules" by changing the
> spinlocks to function calls. Then you'll provide a null stub
> call site
> for running UP, and the real spinlock code for running SMP.
> Unfortunately, this gives the overhead of a function call,
> both for SMP
> and for UP. This overhead is usually _bigger_ than the overhead of a
> inlined spinlock.
Obviously moving the spinlock behind a function call would be slower.
However, I'm not sure whether this would really hurt overall kernel
performance, for two reasons: First, I would think that the requirement to
use the lock instruction would overshadow any function call overhead.
Second, I would guess that minimization of the time the kernel spins on held
locks is much more important than whether acquiring an unheld lock takes 4
instructions or 8.
Anyways, if I ever go back for my masters degree I think modularizing SMP/UP
(and looking at the performance impact) would be an interesting thesis
project ;-)
Regards -- Andy
next reply other threads:[~2001-09-05 21:53 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-09-05 21:18 Grover, Andrew [this message]
2001-09-05 22:11 ` lilo vs other OS bootloaders was: FreeBSD makes progress Alan Cox
2001-09-05 22:13 ` Tim Hockin
-- strict thread matches above, loose matches on Subject: below --
2001-09-04 21:52 Grover, Andrew
2001-09-05 1:51 ` David S. Miller
2001-09-05 8:03 ` Helge Hafting
2001-09-05 14:26 ` Horst von Brand
2001-09-11 22:48 ` Pavel Machek
2001-09-01 14:55 Samium Gromoff
2001-09-01 12:03 ` Peter Wächtler
2001-09-01 12:39 ` Alan Cox
2001-09-01 14:10 ` Rik van Riel
2001-08-31 21:49 Grover, Andrew
2001-08-31 22:40 ` Andreas Dilger
2001-08-31 22:50 ` Alan Cox
2001-09-01 15:50 ` Jamie Lokier
2001-09-08 17:55 ` Eric W. Biederman
2001-09-08 18:55 ` H. Peter Anvin
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