osd/scrub: minimize calls to sysconf() in scrub_load_below_threshold()

Return an 'all is OK' value if the 1min CPU load - even before being
divided by the number of CPUs - is below the configured threshold.
This is a very common case, and avoids the need to call sysconf()
to get the number of CPUs.

Signed-off-by: Ronen Friedman <[email protected]>
(cherry picked from commit 3392bc0)

Author: ronen-fr

src/osd/scrubber/osd_scrub.cc

@@ -306,7 +306,18 @@ std::optional<double> OsdScrub::LoadTracker::update_load_average()
 
 bool OsdScrub::LoadTracker::scrub_load_below_threshold() const
 {
-  // allow scrub if below configured threshold
+  // if the 1-min load average - even before dividing by the number of CPUs -
+  // is below the configured threshold, scrubs are allowed. No need to call
+  // sysconf().
+  if (loadavg_1min < conf->osd_scrub_load_threshold) {
+    dout(20) << fmt::format(
+		    "loadavg {:.3f} < max {:.3f} = yes",
+		    loadavg_1min, conf->osd_scrub_load_threshold)
+	     << dendl;
+    return true;
+  }
+
+  // check the load per CPU
   const long cpus = sysconf(_SC_NPROCESSORS_ONLN);
   const double loadavg_per_cpu = cpus > 0 ? loadavg_1min / cpus : loadavg_1min;
   if (loadavg_per_cpu < conf->osd_scrub_load_threshold) {