Ravikiran G Thirumalai <[email protected]> wrote:
>
> On Wed, Mar 08, 2006 at 04:17:33PM -0500, Benjamin LaHaise wrote:
> > On Wed, Mar 08, 2006 at 01:07:26PM -0800, Ravikiran G Thirumalai wrote:
> >
> > Last time I checked, all the major architectures had efficient local_t
> > implementations. Most of the RISC CPUs are able to do a load / store
> > conditional implementation that is the same cost (since memory barriers
> > tend to be explicite on powerpc). So why not use it?
>
> Then, for the batched percpu_counters, we could gain by using local_t only for
> the UP case. But we will have to have a new local_long_t implementation
> for that. Do you think just one use case of local_long_t warrants for a new
> set of apis?
>
local_t maps onto 32-bit values on 32-bit machines and onto 64-bit values
on 64-bit machines. unsigned longs. I don't quite trust the signedness
handling across all archs.
<looks>
Yes, alpha (for example) went and made its local_t's signed, which is wrong
and dangerous.
ia64 is signed.
mips is signed.
parisc is signed.
s390 is signed.
sparc64 is signed.
x86_64 is signed 32-bit!
All other architectures use unsigned long. A fiasco.
Once decrapify-asm-generic-localh.patch is merged I think all architectures
can and should use asm-generic/local.h.
Until decrapify-asm-generic-localh.patch has been merged and the downstream
arch consolidation has happened and the signedness problems have been
carefully reviewed and fixed I wouldn't go within a mile of local_t.
Once all that is sorted out then yes, it makes sense to convert per-cpu
counters to local_t. Note that local_t is unsigned, and percpu_counter
needs to treat it as signed.
We should also move the out-of-line percpu_counter implementation over to
lib/something.c (in obj-y).
But none of that has anything to do with these patches.
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