x86/pvclock: Improve atomic update of last_value in pvclock_clocksource_read()

Improve atomic update of last_value in pvclock_clocksource_read:

- Atomic update can be skipped if the "last_value" is already
  equal to "ret".

- The detection of atomic update failure is not correct. The value,
  returned by atomic64_cmpxchg should be compared to the old value
  from the location to be updated. If these two are the same, then
  atomic update succeeded and "last_value" location is updated to
  "ret" in an atomic way. Otherwise, the atomic update failed and
  it should be retried with the value from "last_value" - exactly
  what atomic64_try_cmpxchg does in a correct and more optimal way.

Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/r/[email protected]

0 files changed, 0 insertions, 0 deletions