Add cpuset size information to the FJR.

We have found that it's difficult to detect when the cpuset (set by
some batch systems) is limiting the number of cores we can run on.

In one extreme case, the batch system arguments were being done
incorrectly and 32 cores worth of CMS jobs were being forced onto a
single core.

This records the current cpuset size to the FJR when CPU information
reporting is enabled.  The resulting line looks like:

    <Metric Name="cpusetCount" Value="1"/>

With this, we hope that experts are more likely to notice that the
cpuset is different from expectations

FWCore/Services/plugins/CPU.cc

@@ -27,6 +27,11 @@
 #include <sstream>
 #include <set>
 
+#ifdef __linux__
+#include <sched.h>
+#include <errno.h>
+#endif
+
 namespace edm {
 
   namespace service {
@@ -102,6 +107,36 @@ namespace edm {
 	}
 	return aux;
       }
+
+      // Determine the CPU set size; if this can be successfully determined, then this
+      // returns true.
+      bool getCpuSetSize(unsigned &set_size) {
+#ifdef __linux__
+        cpu_set_t *cpusetp;
+        unsigned current_size = 128;
+        unsigned cpu_count = 0;
+        while (current_size*2 > current_size) {
+          cpusetp = CPU_ALLOC(current_size);
+          CPU_ZERO_S(CPU_ALLOC_SIZE(current_size), cpusetp);
+
+          if (sched_getaffinity(0, CPU_ALLOC_SIZE(current_size), cpusetp)) {
+            CPU_FREE(cpusetp);
+            if (errno == EINVAL) {
+              current_size *= 2;
+              continue;
+            }
+            return false;
+          }
+          cpu_count = CPU_COUNT_S(CPU_ALLOC_SIZE(current_size), cpusetp);
+          CPU_FREE(cpusetp);
+          break;
+        }
+        set_size = cpu_count;
+        return true;
+#else
+        return false;
+#endif
+      }
     } // namespace {}
 
 
@@ -225,6 +260,10 @@ namespace edm {
 	}
 	reportCPUProperties.insert(std::make_pair("CPUModels", CPUModels));
 
+        unsigned set_size = -1;
+        if (getCpuSetSize(set_size)) {
+          reportCPUProperties.insert(std::make_pair("cpusetCount", i2str(set_size)));
+        }
 
 	reportSvc->reportPerformanceSummary("SystemCPU", reportCPUProperties);