On 05/25/2011 03:17 PM, Dave Martin wrote:
On Wed, May 25, 2011 at 12:58:30PM +0100, David Gilbert wrote:
On 25 May 2011 04:45, Nicolas Pitre<nicolas.pi...@linaro.org> wrote:
FWIW, here's what the kernel part might look like, i.e. for
compatibility with pre ARMv6k systems (beware, only compile tested):
OK, so that makes a eglibc part for that pretty easy.
For things like fetch_and_add (which I can see membase needs)
would you expect implementation using this cmpxchg so it has a fall
back or just to use ldrexd directly which I assume would be somewhat
more efficient.
(Question holds for both eglibc and gcc's __sync_*)
It depends on the baseline architecture for the build.
An eglibc built for ARMv6 and above would need to call the helper by
default, though it could also use ldrexd/strexd if it determines at run-
time that this is supported by the CPU.
Similarly, if GCC is building for -march=marmv7-a it can inline the
atomics directly using ldrex/strex and friends, but for -march=armv6 it
will need to call helpers via libgcc.
I would have thought that the libc does not decide this directly but
just calls the GCC __sync_* routines (if build with a GCC that supports
them). Then the GCC decides whether to inline them using ldrexd/strexd
(ARMv6+) or emit calls to libgcc which calls the kernel helpers.
Regards
Ken
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