This commit fixes a potential racey-add that could occur if
multiple service-lcores were executing the same MT-safe service
at the same time, with service statistics collection enabled.
Because multiple threads can run and execute the service, the
stats values can have multiple writer threads, resulting in the
requirement of using atomic addition for correctness.
Note that when a MT unsafe service is executed, a spinlock is
held, so the stats increments are protected. This fact is used
to avoid executing atomic add instructions when not required.
Regular reads and increments are used, and only the store is
specified as atomic, reducing perf impact on e.g. x86 arch.
This patch causes a 1.25x increase in cycle-cost for polling a
MT safe service when statistics are enabled. No change was seen
for MT unsafe services, or when statistics are disabled.
Fixes: 21698354c8 ("service: introduce service cores concept")
Reported-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Suggested-by: Morten Brørup <mb@smartsharesystems.com>
Suggested-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
99e4e84047