[PATCH] powerpc: Optimise the 64bit optimised __clear_user

David Laight David.Laight at ACULAB.COM
Thu Jun 7 18:41:35 EST 2012


> -----Original Message-----
> From: Linuxppc-dev 
> [mailto:linuxppc-dev-bounces+david.laight=aculab.com at lists.ozl
abs.org] On Behalf Of Benjamin Herrenschmidt
> Sent: 07 June 2012 07:40
> To: Michael Neuling
> Cc: michael at ellerman.id.au; paulus at samba.org; Anton 
> Blanchard; olof at lixom.net; linuxppc-dev at lists.ozlabs.org
> Subject: Re: [PATCH] powerpc: Optimise the 64bit optimised 
> __clear_user
> On Thu, 2012-06-07 at 16:05 +1000, Michael Neuling wrote:
> > One problem with this is when we construct the 
> instructions, like using
> > anything from ppc-opcode.h.  eg. using PPC_POPCNTB would 
> need to go from:
> >     PPC_POPCNTB(r3,r3) 
> > to:
> >     PPC_POPCNTB(3,3) 
> > Which is less readable IMHO.
> Yes, I know. Not much to do about this, but it might still be 
> worth it,
> how much time wasted due to mixing up or with ori in asm somewhere ?
> One option would be to #define R3 (or _r3) for use in those macros so
> we still have something nicer than just "3"... oh well.

You then need to catch all the other bugs where a register
is being used instead of a constant.
Time to make the assembler require %r0 (etc)


More information about the Linuxppc-dev mailing list