contrib/plugins: allow setting of instructions per quantum

The default is we update time every 1/10th of a second or so. However
for some cases we might want to update time more frequently. Allow
this to be set via the command line through the ipq argument.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20250603110204.838117-7-alex.bennee@linaro.org>

contrib/plugins/ips.c

@@ -145,6 +145,8 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
                                            const qemu_info_t *info, int argc,
                                            char **argv)
 {
+    bool ipq_set = false;
+
     for (int i = 0; i < argc; i++) {
         char *opt = argv[i];
         g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
@@ -175,6 +177,14 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
                     return -1;
                 }
             }
+        } else if (g_strcmp0(tokens[0], "ipq") == 0) {
+            max_insn_per_quantum = g_ascii_strtoull(tokens[1], NULL, 10);
+
+            if (!max_insn_per_quantum) {
+                fprintf(stderr, "bad ipq value: %s\n", tokens[0]);
+                return -1;
+            }
+            ipq_set = true;
         } else {
             fprintf(stderr, "option parsing failed: %s\n", opt);
             return -1;
@@ -182,7 +192,10 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
     }
 
     vcpus = qemu_plugin_scoreboard_new(sizeof(vCPUTime));
-    max_insn_per_quantum = max_insn_per_second / NUM_TIME_UPDATE_PER_SEC;
+
+    if (!ipq_set) {
+        max_insn_per_quantum = max_insn_per_second / NUM_TIME_UPDATE_PER_SEC;
+    }
 
     if (max_insn_per_quantum == 0) {
         fprintf(stderr, "minimum of %d instructions per second needed\n",

docs/about/emulation.rst

@@ -811,6 +811,10 @@ This plugin can limit the number of Instructions Per Second that are executed::
   * - ips=N
     - Maximum number of instructions per cpu that can be executed in one second.
       The plugin will sleep when the given number of instructions is reached.
+  * - ipq=N
+    - Instructions per quantum. How many instructions before we re-calculate time.
+      The lower the number the more accurate time will be, but the less efficient the plugin.
+      Defaults to ips/10
 
 Other emulation features
 ------------------------