xenpm, x86: Fix reporting of idle state average residency times

If CPU stays in the same idle state for the full duration of
xenpm sample then average residency may not be reported correctly
since usage counter will not be incremented.

In addition, in order to calculate averages correctly residence
time and usage counter should be read and written atomically.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@amd.com>
Committed-by: Keir Fraser <keir@xen.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/tools/misc/xenpm.c b/tools/misc/xenpm.c
index 65876fe370..e6fa942828 100644
--- a/tools/misc/xenpm.c
+++ b/tools/misc/xenpm.c
@@ -389,7 +389,14 @@ static void signal_int_handler(int signo)
                 res = ( diff >= 0 ) ? diff : 0;
                 triggers = cxstat_end[i].triggers[j] -
                     cxstat_start[i].triggers[j];
-                avg_res = (triggers==0) ? 0: (double)res/triggers/1000000.0;
+                /* 
+                 * triggers may be zero if the CPU has been in this state for
+                 * the whole sample or if it never entered the state
+                 */
+                if ( triggers == 0 && cxstat_end[i].last == j )
+                    avg_res =  (double)sum_cx[i]/1000000.0;
+                else
+                    avg_res = (triggers==0) ? 0: (double)res/triggers/1000000.0;
                 printf("  C%d\t%"PRIu64"\t(%5.2f%%)\t%.2f\n", j, res/1000000UL,
                         100 * res / (double)sum_cx[i], avg_res );
             }