Re: CVS commit: src/sys/kern

[David Laight <david%l8s.co.uk@localhost>]

On Thu, Jun 02, 2011 at 09:21:11PM +0100, David Laight wrote:
> On Thu, Jun 02, 2011 at 06:54:44PM +0000, David Laight wrote:
> > Module Name:        src
> > Committed By:       dsl
> > Date:               Thu Jun  2 18:54:44 UTC 2011
> > 
> > Modified Files:
> >     src/sys/kern: vfs_syscalls.c
> > 
> > Log Message:
> > Fix type in comment
> > (before I replace the 'l' with 'curlwp')
> 
> Actually I've thought about this some more.
> While, on the face of it, removing the 'struct lwp *' parameter to all system
> calls might seem an optimisation, I suspect that, especially on systems where
> arguments are passed in registers, it is a pessimisation.
> 
> Passing 'l' is a register rename (or copy) so is almost zero cost.
> 
> Recovering curlwp may involve a function call, and is, at best, a real
> memory access of global data (possibly via an asm statement) that will
> be slow and multiple accesses might need caching in a local anyway.

Well, an amd64 GENERIC kernel grows by 1.5k, and I've given up trying to get
an i386 MONOLITHIC to compile - too much crap in compat.

        David

-- 
David Laight: david%l8s.co.uk@localhost