Linus Torvalds wrote:
On Mon, 14 Nov 2005, Gerd Knorr wrote:
Throwing another patch into the discussion ;)
Ouch, this one is really ugly.
I somehow expected that answer, it took me quite some time to figure
what the patch does. It certainly needs at least a number of cleanups
before I'd consider it mergable. The alternative() macro is much easier
to read.
If you want to go this way, then you should instead add an X86_FEATURE_SMP
that gets cleared on UP and on SMP with just one core (and detect when CPU
hotplug ain't gonna happen ;), and then do
Well, the "no hotplug" probably is exactly the reason why the patch
doesn't use the existing alternatives mechanism, it's a boot-time
one-way ticket. The xenified linux kernel actually switches both ways
at runtime if you plug in/out a second virtual CPU.
#ifdef CONFIG_SMP
#define smp_alternative(x,y) alternative(x,y,X86_FEATURE_SMP)
#else
#define smp_alternative(x,y) asm(x)
#endif
I don't like the idea very much. That covers only 50% of what the patch
does, you can patch SMP => UP but not the other way around. Doesn't
matter much on real hardware, but for virtual it is quite useful.
or something similar, instead of creating a totally new infrastructure to
do the thing that "alternative()" already does.
Yep, extending alternatives is probably better than duplicating the
code. Maybe having some alternative_smp() macro which places both code
versions into the .altinstr_replacement table? If that sounds ok I'll
try to come up with a experimental patch. If not: other ideas are welcome.
cheers,
Gerd
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