cvs commit: src/sys/kern subr_witness.c src/sys/sys _lock.h lock.h

[Andre Oppermann]

John Baldwin wrote:
> 
> On Monday 05 December 2005 03:45 pm, John Baldwin wrote:
> > jhb         2005-12-05 20:45:24 UTC
> >
> >   FreeBSD src repository
> >
> >   Modified files:
> >     sys/kern             subr_witness.c
> >     sys/sys              _lock.h lock.h
> >   Log:
> >   Tweak witness handling of lock object to shave 2 pointers off of each
> >   lock object (and thus off of each mutex and sx lock):
> >
> >   ...
> >
> >   With these changes, struct mtx shrinks from 36 to 28 bytes on 32-bit
> >   platforms and from 72 to 56 bytes on 64-bit platforms.  Note that this
> >   commit will completely and utterly destroy the kernel ABI, so no MFC.
> >
> >   Tested on:      alpha, amd64, i386, sparc64
> 
> andre@ reported a 5% perf increase from this change on at least one network
> benchmark.

I tested only with WITNESS enabled and there it did in fact make a 5%
difference on a HTTP connection performance test over the loopback
interface.  It is mostly limited by lock performance and I was measuring
only 33 instructions on average between two lock operations (lock or
unlock).

-- 
Andre