perf: add context_switches software perf event support

This patch adds support and documentation
for the context_switches perf event.
Signed-off-by: NNitesh Konkar <nitkon12@linux.vnet.ibm.com>

docs/formatdomain.html.in

@@ -1950,6 +1950,7 @@
   <event name='cpu_clock' enabled='no'/>
   <event name='task_clock' enabled='no'/>
   <event name='page_faults' enabled='no'/>
+  <event name='context_switches' enabled='no'/>
 </perf>
 ...
 </pre>
@@ -2049,6 +2050,12 @@
           types of page faults</td>
       <td><code>perf.page_faults</code></td>
     </tr>
+    <tr>
+      <td><code>context_switches</code></td>
+      <td>the count of context switches by applications running on
+          the platform</td>
+      <td><code>perf.context_switches</code></td>
+    </tr>
   </table>
 
     <h3><a name="elementsDevices">Devices</a></h3>

docs/schemas/domaincommon.rng

@@ -436,6 +436,7 @@
               <value>cpu_clock</value>
               <value>task_clock</value>
               <value>page_faults</value>
+              <value>context_switches</value>
             </choice>
           </attribute>
           <attribute name="enabled">

include/libvirt/libvirt-domain.h

@@ -2220,6 +2220,16 @@ void virDomainStatsRecordListFree(virDomainStatsRecordPtr *stats);
 */
 # define VIR_PERF_PARAM_PAGE_FAULTS "page_faults"
 
+/**
+ * VIR_PERF_PARAM_CONTEXT_SWITCHES:
+ *
+ * Macro for typed parameter name that represents context_switches
+ * perf event which can be used to measure the count of context
+ * switches by applications running on the platform. It corresponds
+ * to the "perf.context_switches" field in the *Stats APIs.
+ */
+# define VIR_PERF_PARAM_CONTEXT_SWITCHES "context_switches"
+
 
 int virDomainGetPerfEvents(virDomainPtr dom,
                            virTypedParameterPtr *params,

src/libvirt-domain.c

@@ -11256,6 +11256,9 @@ virConnectGetDomainCapabilities(virConnectPtr conn,
  *                         It is produced by the task_clock perf event.
  *     "perf.page_faults" - The count of page faults as unsigned long long.
  *                          It is produced by the page_faults perf event
+ *     "perf.context_switches" - The count of context switches as unsigned long
+ *                               long. It is produced by the context_switches
+ *                               perf event.
  *
  * Note that entire stats groups or individual stat fields may be missing from
  * the output in case they are not supported by the given hypervisor, are not

src/qemu/qemu_driver.c

@@ -9570,6 +9570,7 @@ qemuDomainSetPerfEvents(virDomainPtr dom,
                                VIR_PERF_PARAM_CPU_CLOCK, VIR_TYPED_PARAM_BOOLEAN,
                                VIR_PERF_PARAM_TASK_CLOCK, VIR_TYPED_PARAM_BOOLEAN,
                                VIR_PERF_PARAM_PAGE_FAULTS, VIR_TYPED_PARAM_BOOLEAN,
+                               VIR_PERF_PARAM_CONTEXT_SWITCHES, VIR_TYPED_PARAM_BOOLEAN,
                                NULL) < 0)
         return -1;
 

src/util/virperf.c

@@ -44,7 +44,8 @@ VIR_ENUM_IMPL(virPerfEvent, VIR_PERF_EVENT_LAST,
               "branch_instructions", "branch_misses",
               "bus_cycles", "stalled_cycles_frontend",
               "stalled_cycles_backend", "ref_cpu_cycles",
-              "cpu_clock", "task_clock", "page_faults");
+              "cpu_clock", "task_clock", "page_faults",
+              "context_switches");
 
 struct virPerfEvent {
     int type;
@@ -122,6 +123,9 @@ static struct virPerfEventAttr attrs[] = {
     {.type = VIR_PERF_EVENT_PAGE_FAULTS,
      .attrType = PERF_TYPE_SOFTWARE,
      .attrConfig = PERF_COUNT_SW_PAGE_FAULTS},
+    {.type = VIR_PERF_EVENT_CONTEXT_SWITCHES,
+     .attrType = PERF_TYPE_SOFTWARE,
+     .attrConfig = PERF_COUNT_SW_CONTEXT_SWITCHES},
 };
 typedef struct virPerfEventAttr *virPerfEventAttrPtr;
 

src/util/virperf.h

@@ -50,6 +50,7 @@ typedef enum {
     VIR_PERF_EVENT_CPU_CLOCK,   /* Count of cpu clock time*/
     VIR_PERF_EVENT_TASK_CLOCK,   /* Count of task clock time*/
     VIR_PERF_EVENT_PAGE_FAULTS,   /* Count of total page faults */
+    VIR_PERF_EVENT_CONTEXT_SWITCHES,   /* Count of context switches */
 
     VIR_PERF_EVENT_LAST
 } virPerfEventType;

tests/genericxml2xmlindata/generic-perf.xml

@@ -29,6 +29,7 @@
     <event name='cpu_clock' enabled='yes'/>
     <event name='task_clock' enabled='yes'/>
     <event name='page_faults' enabled='yes'/>
+    <event name='context_switches' enabled='yes'/>
   </perf>
   <devices>
   </devices>

tools/virsh.pod

@@ -967,6 +967,7 @@ I<--perf> returns the statistics of all enabled perf events:
  "perf.cpu_clock" - the count of cpu clock time
  "perf.task_clock" - the count of task clock time
  "perf.page_faults" - the count of page faults
+ "perf.context_switches" - the count of context switches
 
 See the B<perf> command for more details about each event.
 
@@ -2342,6 +2343,8 @@ B<Valid perf event names>
                applications running on the platform.
   page_faults - Provides the count of page faults by
                 applications running on the platform.
+  context_switches - Provides the count of context switches
+                     by applications running on the platform.
 
 B<Note>: The statistics can be retrieved using the B<domstats> command using
 the I<--perf> flag.