Re: [patch 2/8] Implement always-locked bit ops, for memory shared with an SMP hypervisor.

Christoph Lameter
2006-08-03T05:54:31Z

On Thu, 3 Aug 2006, Andi Kleen wrote:

> > I still wonder why you are so focused on ifdefs. Why would we need those?
>
> Because the Xen drivers will run on a couple of architectures, including
> IA64 and PPC.
>
> If IA64 or PPC didn't implement at least wrappers for the sync ops
> then they would all need special ifdefs to handle this.

No they would just need to do an #include <xen-bitops.h>

> > Maybe the best thing would be to have proper atomic ops in UP mode on
> > i386? The current way of just dropping the lock bit is the source of the
> > troubles.
>
> It's a huge performance difference.

I understand but why dont we use regular ops explicitly
instead of hacking the atomic ops. Then we would not have unhack them now.

> > Just adding a single line #include <asm/xen-bitops.h> to drivers that need
> > this functionality is not an undue burden for the drivers that support
> > Xen. They have to use special _xxx bitops anyways.
>
> Ok it could be put into a separate file (although with a neutral name)
>
> But you would still need to add that to IA64, PPC etc. too, so it
> would only avoid adding a single to the other architectures.

Could we not just add one fallback definition to asm-generic?