[Qemu-devel] [RFC v2 08/11] tcg: add options for enabling MTTCG

["Alex Bennée" <alex.bennee@linaro.org>]

From: KONRAD Frederic <fred.konrad@greensocs.com>

We know there will be cases where MTTCG won't work until additional work
is done in the front/back ends to support. It will however be useful to
be able to turn it on.

As a result MTTCG will default to off unless the combination is
supported. However the user can turn it on for the sake of testing.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
[AJB: move to -tcg mttcg=on/off, defaults]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v1:
  - merge with add mttcg option.
  - update commit message
v2:
  - machine_init->opts_init
---
 cpus.c                | 43 +++++++++++++++++++++++++++++++++++++++++++
 include/qom/cpu.h     | 14 ++++++++++++++
 include/sysemu/cpus.h |  2 ++
 qemu-options.hx       | 14 ++++++++++++++
 vl.c                  | 12 +++++++++++-
 5 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/cpus.c b/cpus.c
index 46732a5..8d27fb0 100644
--- a/cpus.c
+++ b/cpus.c
@@ -25,6 +25,7 @@
 /* Needed early for CONFIG_BSD etc. */
 #include "qemu/osdep.h"
 
+#include "qemu/config-file.h"
 #include "monitor/monitor.h"
 #include "qapi/qmp/qerror.h"
 #include "qemu/error-report.h"
@@ -146,6 +147,48 @@ typedef struct TimersState {
 } TimersState;
 
 static TimersState timers_state;
+static bool mttcg_enabled;
+
+static QemuOptsList qemu_tcg_opts = {
+    .name = "tcg",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_tcg_opts.head),
+    .desc = {
+        {
+            .name = "mttcg",
+            .type = QEMU_OPT_BOOL,
+            .help = "Enable/disable multi-threaded TCG",
+        },
+        { /* end of list */ }
+    },
+};
+
+static void tcg_register_config(void)
+{
+    qemu_add_opts(&qemu_tcg_opts);
+}
+
+opts_init(tcg_register_config);
+
+static bool default_mttcg_enabled(void)
+{
+    /*
+     * TODO: Check if we have a chance to have MTTCG working on this guest/host.
+     *       Basically is the atomic instruction implemented? Is there any
+     *       memory ordering issue?
+     */
+    return false;
+}
+
+void qemu_tcg_configure(QemuOpts *opts)
+{
+    mttcg_enabled = qemu_opt_get_bool(opts, "mttcg", default_mttcg_enabled());
+}
+
+bool qemu_tcg_mttcg_enabled(void)
+{
+    return mttcg_enabled;
+}
+
 
 int64_t cpu_get_icount_raw(void)
 {
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 13eeaae..5e3826c 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -369,6 +369,20 @@ extern struct CPUTailQ cpus;
 extern __thread CPUState *current_cpu;
 
 /**
+ * qemu_tcg_enable_mttcg:
+ * Enable the MultiThread TCG support.
+ */
+void qemu_tcg_enable_mttcg(void);
+
+/**
+ * qemu_tcg_mttcg_enabled:
+ * Check whether we are running MultiThread TCG or not.
+ *
+ * Returns: %true if we are in MTTCG mode %false otherwise.
+ */
+bool qemu_tcg_mttcg_enabled(void);
+
+/**
  * cpu_paging_enabled:
  * @cpu: The CPU whose state is to be inspected.
  *
diff --git a/include/sysemu/cpus.h b/include/sysemu/cpus.h
index 3d1e5ba..606426f 100644
--- a/include/sysemu/cpus.h
+++ b/include/sysemu/cpus.h
@@ -26,4 +26,6 @@ extern int smp_threads;
 
 void list_cpus(FILE *f, fprintf_function cpu_fprintf, const char *optarg);
 
+void qemu_tcg_configure(QemuOpts *opts);
+
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index a770086..4eca704 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3224,6 +3224,20 @@ Attach to existing xen domain.
 xend will use this when starting QEMU (XEN only).
 ETEXI
 
+DEF("tcg", HAS_ARG, QEMU_OPTION_tcg, \
+    "-tcg [mttcg=on|off] control TCG options\n", QEMU_ARCH_ALL)
+STEXI
+@item -tcg
+@findex -tcg
+@table @option
+@item mttcg=[on|off]
+Control multi-threaded TCG. By default QEMU will enable multi-threaded
+emulation for front/back-end combinations that are known to work. The
+user may enable it against the defaults however odd guest behaviour
+may occur.
+@end table
+ETEXI
+
 DEF("no-reboot", 0, QEMU_OPTION_no_reboot, \
     "-no-reboot      exit instead of rebooting\n", QEMU_ARCH_ALL)
 STEXI
diff --git a/vl.c b/vl.c
index bd81ea9..51bbdbc 100644
--- a/vl.c
+++ b/vl.c
@@ -2961,7 +2961,8 @@ int main(int argc, char **argv, char **envp)
     const char *boot_once = NULL;
     DisplayState *ds;
     int cyls, heads, secs, translation;
-    QemuOpts *hda_opts = NULL, *opts, *machine_opts, *icount_opts = NULL;
+    QemuOpts *opts, *machine_opts;
+    QemuOpts *hda_opts = NULL, *icount_opts = NULL, *tcg_opts = NULL;
     QemuOptsList *olist;
     int optind;
     const char *optarg;
@@ -3750,6 +3751,13 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_no_reboot:
                 no_reboot = 1;
                 break;
+            case QEMU_OPTION_tcg:
+                tcg_opts = qemu_opts_parse_noisily(qemu_find_opts("tcg"),
+                                                   optarg, false);
+                if (!tcg_opts) {
+                    exit(1);
+                }
+                break;
             case QEMU_OPTION_no_shutdown:
                 no_shutdown = 1;
                 break;
@@ -4028,6 +4036,8 @@ int main(int argc, char **argv, char **envp)
      */
     loc_set_none();
 
+    qemu_tcg_configure(tcg_opts);
+
     replay_configure(icount_opts);
 
     machine_class = select_machine();
-- 
2.7.4