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author | Uros Bizjak <ubizjak@gmail.com> | 2024-04-22 15:00:38 +0300 |
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committer | Ingo Molnar <mingo@kernel.org> | 2024-04-24 12:46:28 +0300 |
commit | 94af3a04e3f386d4f060d903826e85aa006ce252 (patch) | |
tree | 5d1b4e482490d0f6591bb6a90630f69faf65a95a /Documentation/devicetree/bindings/openrisc | |
parent | 33eb8ab4ec83cf0975d0113966c7e71cd6be60b2 (diff) | |
download | linux-94af3a04e3f386d4f060d903826e85aa006ce252.tar.xz |
locking/qspinlock/x86: Micro-optimize virt_spin_lock()
Optimize virt_spin_lock() to use simpler and faster:
atomic_try_cmpxchg(*ptr, &val, new)
instead of:
atomic_cmpxchg(*ptr, val, new) == val
The x86 CMPXCHG instruction returns success in the ZF flag, so
this change saves a compare after the CMPXCHG.
Also optimize retry loop a bit. atomic_try_cmpxchg() fails iff
&lock->val != 0, so there is no need to load and compare the
lock value again - cpu_relax() can be unconditinally called in
this case. This allows us to generate optimized:
1f: ba 01 00 00 00 mov $0x1,%edx
24: 8b 03 mov (%rbx),%eax
26: 85 c0 test %eax,%eax
28: 75 63 jne 8d <...>
2a: f0 0f b1 13 lock cmpxchg %edx,(%rbx)
2e: 75 5d jne 8d <...>
...
8d: f3 90 pause
8f: eb 93 jmp 24 <...>
instead of:
1f: ba 01 00 00 00 mov $0x1,%edx
24: 8b 03 mov (%rbx),%eax
26: 85 c0 test %eax,%eax
28: 75 13 jne 3d <...>
2a: f0 0f b1 13 lock cmpxchg %edx,(%rbx)
2e: 85 c0 test %eax,%eax
30: 75 f2 jne 24 <...>
...
3d: f3 90 pause
3f: eb e3 jmp 24 <...>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240422120054.199092-1-ubizjak@gmail.com
Diffstat (limited to 'Documentation/devicetree/bindings/openrisc')
0 files changed, 0 insertions, 0 deletions