Improve the scalability of the fpswa code that rate-limits
logging of messages.
There are 2 distinctly different problems in this code.
1) If prctl is used to disable logging, last_time is never
updated. The result is that fpu_swa_count is zeroed out on
EVERY fp fault. This causes a very very hot cache line.
The fix reduces the wallclock time of a 1024p FP exception test
from 28734 sec to 19 sec!!!
2) On VERY large systems, excessive messages are logged because
multiple cpus can each reset or increment fpu_swa_count at
about the same time. The result is that hundreds of messages
are logged each second. The fixes reduces the logging rate
to ~1 per second.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
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