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SubjectRe: [PATCH][2.6] Completely out of line spinlocks / x86_64
On Mon, Aug 09, 2004 at 01:23:08PM +0200, Andi Kleen wrote:
> On Sun, 8 Aug 2004 02:08:30 -0400 (EDT)
> Zwane Mwaikambo <zwane@linuxpower.ca> wrote:
>
> > arch/x86_64/Kconfig | 10 ++++++++++
> > arch/x86_64/lib/Makefile | 1 +
> > arch/x86_64/lib/spinlock.c | 38 ++++++++++++++++++++++++++++++++++++++
> > include/asm-x86_64/spinlock.h | 22 ++++++++++++++++++++--
> > 4 files changed, 69 insertions(+), 2 deletions(-)
> >
> > Index: linux-2.6.8-rc3-mm1-amd64/arch/x86_64/Kconfig
> > ===================================================================
> > RCS file: /home/cvsroot/linux-2.6.8-rc3-mm1/arch/x86_64/Kconfig,v
> > retrieving revision 1.1.1.1
> > diff -u -p -B -r1.1.1.1 Kconfig
> > --- linux-2.6.8-rc3-mm1-amd64/arch/x86_64/Kconfig 5 Aug 2004 16:37:48 -0000 1.1.1.1
> > +++ linux-2.6.8-rc3-mm1-amd64/arch/x86_64/Kconfig 7 Aug 2004 22:47:30 -0000
> > @@ -438,6 +438,16 @@ config DEBUG_SPINLOCK
> > best used in conjunction with the NMI watchdog so that spinlock
> > deadlocks are also debuggable.
> >
> > +config COOL_SPINLOCK
> > + bool "Completely out of line spinlocks"
> > + depends on SMP
> > + default y
> > + help
> > + Say Y here to build spinlocks which have common text for contended
> > + and uncontended paths. This reduces kernel text size by at least
> > + 50k on most configurations, plus there is the additional benefit
> > + of better cache utilisation.
>
> I think the 50k number is wrong. I took a look at it and the big
> difference is only seen when you enable interrupts during spinning, which
> we didn't do before. If you compare it to the old implementation the
> difference is much less.
>
> I don't really like the config option. Either it's a good idea
> then it should be done by default without option or it should not be done at all.
>
> Did you do any lock intensive benchmarks that could show a slowdown?

Out of curiosity, also, have you ran any lock intensive benchmarks to get some
numbers out of the increased cacheline hits due to uninlining?

I think you can measure the hits/misses precisely with Mikael's perfcounters.

>
> > Index: linux-2.6.8-rc3-mm1-amd64/arch/x86_64/lib/spinlock.c
> > ===================================================================
> > RCS file: linux-2.6.8-rc3-mm1-amd64/arch/x86_64/lib/spinlock.c
> > diff -N linux-2.6.8-rc3-mm1-amd64/arch/x86_64/lib/spinlock.c
> > --- /dev/null 1 Jan 1970 00:00:00 -0000
> > +++ linux-2.6.8-rc3-mm1-amd64/arch/x86_64/lib/spinlock.c 8 Aug 2004 05:39:04 -0000
> > @@ -0,0 +1,38 @@
> > +#include <linux/module.h>
>
> You should make this file assembly only.
-
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