Store time of the previous process scan

The difference of scans is useful for utilization calculations.

To avoid divisions by 0 on first scan set monotonicMs also on first
scan.

2 files changed, 8 insertions, 3 deletions

diff --git a/Machine.c b/Machine.c
index 44aa27c8..6beb47b4 100644
--- a/Machine.c
+++ b/Machine.c
@@ -99,10 +99,14 @@ void Machine_scanTables(Machine* this) {
    // set scan timestamp
    static bool firstScanDone = false;
 
-   if (firstScanDone)
-      Platform_gettime_monotonic(&this->monotonicMs);
-   else
+   if (firstScanDone) {
+      this->prevMonotonicMs = this->monotonicMs;
+   } else {
+      this->prevMonotonicMs = 0;
       firstScanDone = true;
+   }
+   Platform_gettime_monotonic(&this->monotonicMs);
+   assert(this->monotonicMs > this->prevMonotonicMs);
 
    this->maxUserId = 0;
    Row_resetFieldWidths();
diff --git a/Machine.h b/Machine.h
index 419911c3..f7f82afa 100644
--- a/Machine.h
+++ b/Machine.h
@@ -41,6 +41,7 @@ typedef struct Machine_ {
    struct timeval realtime;   /* time of the current sample */
    uint64_t realtimeMs;       /* current time in milliseconds */
    uint64_t monotonicMs;      /* same, but from monotonic clock */
+   uint64_t prevMonotonicMs;  /* time in milliseconds from monotonic clock of previous scan */
 
    int64_t iterationsRemaining;