On MIPS64 we have spinlocks that are 32b in size and an efficient
cmpxchg64 implementation, so we qualify to make use of cmpxchg backed
lockrefs. Select the ARCH_USE_CMPXCHG_LOCKREF Kconfig symbol and provide
a trivial implementation of arch_spin_value_unlocked to satisfy the
lockref code.
Using Linus' simple testcase from
http://article.gmane.org/gmane.linux.file-systems/77466 on a dual core
system with an in-development MIPS64 CPU running on FPGA I see around an
8% gain:
Pre-patch:
Total loops: 252698
Total loops: 251482
Total loops: 250806
Total loops: 252885
Total loops: 251666
Post-patch:
Total loops: 273728
Total loops: 269932
Total loops: 269341
Total loops: 275004
Total loops: 270208
[ralf@linux-mips.org: Fixed conflict.]
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Cc: Maciej W. Rozycki <macro@codesourcery.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/10810/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
5fac4f7ac0