Re: [PATCH 0/9] x86-64 put current in r10

[Kyle Moffett]

On Nov 30, 2005, at 11:22:48, Randy.Dunlap wrote:
> On Wed, 30 Nov 2005, Jari Ruusu wrote:
>
> > Benjamin LaHaise wrote:
> > > The following emails contain the patches to convert x86-64 to  
> > > store current
> > > in r10 (also at http://www.kvack.org/~bcrl/patches/v2.6.15-rc3/).
> > [snip]
> > > No benchmarks that I am aware of show regressions with this change.
> >
> > Ben,
> > Your patch breaks all out-of-tree amd64 assembler code used in  
> > kernel. r10 register is one of those registers that does not need  
> > to be preserved across function calls, and reserving that register  
> > for other purpose means that all assembler code using r10 in  
> > kernel must be rewritten. This is deeply unfunny.
> >
> > Andi,
> > Please don't apply Ben's patch. It is already bad enough having to  
> > deal with two incompatible calling conventions on 32 bit x86.
>
> Just for the sake of understanding the current kernel release  
> process, when would something like this be acceptable/possible?   
> Would it require a Linux 3.0 version, or at least a 2.8?

It's perfectly acceptable in 2.6, assuming it's properly divided up  
into small discrete changes and spends a bit of time in -mm first to  
work out the bugs.  If people want to maintain out-of-tree drivers,  
especially those using assembly, when things break they get to keep  
both pieces.  This patch produces a rather large space savings and  
speeds things up to boot, and I would support it being pushed to  
Linus during the 2.6.16 merge window assuming it stands up to abuse  
in -mm for a bit.

Cheers,
Kyle Moffett

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