[Qemu-devel] [RFC v4 13/28] 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 -accel tcg,thread=multi|single, defaults]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v1:
  - merge with add mttcg option.
  - update commit message
v2:
  - machine_init->opts_init
v3:
  - moved from -tcg to -accel tcg,thread=single|multi
  - fix checkpatch warnings
v4:
  - make mttcg_enabled extern, qemu_tcg_mttcg_enabled() now just macro
  - qemu_tcg_configure now propagates Error instead of exiting
  - better error checking of thread=foo
  - use CONFIG flags for default_mttcg_enabled()
  - disable mttcg with icount, error if both forced on
---
 cpus.c                | 40 ++++++++++++++++++++++++++++++++++++++++
 include/qom/cpu.h     |  9 +++++++++
 include/sysemu/cpus.h |  2 ++
 qemu-options.hx       | 20 ++++++++++++++++++++
 vl.c                  | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 5 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/cpus.c b/cpus.c
index 0ff51ea..b5b45b8 100644
--- a/cpus.c
+++ b/cpus.c
@@ -25,6 +25,7 @@
 /* Needed early for CONFIG_BSD etc. */
 #include "qemu/osdep.h"
 #include "qemu-common.h"
+#include "qemu/config-file.h"
 #include "cpu.h"
 #include "monitor/monitor.h"
 #include "qapi/qmp/qerror.h"
@@ -148,6 +149,45 @@ typedef struct TimersState {
 } TimersState;
 
 static TimersState timers_state;
+bool mttcg_enabled;
+
+/*
+ * We default to false if we know other options have been enabled
+ * which are currently incompatible with MTTCG. Otherwise when each
+ * guest (target) and host has been updated to support:
+ *   - atomic instructions
+ *   - memory ordering
+ * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
+ * and generated config-host.mak fragments.
+ */
+static bool default_mttcg_enabled(void)
+{
+    if (qemu_find_opts("icount")) {
+        return false;
+    } else {
+#if defined(CONFIG_MTTCG_TARGET) && defined(CONFIG_MTTCG_HOST)
+        return true;
+#else
+        return false;
+#endif
+    }
+}
+
+void qemu_tcg_configure(QemuOpts *opts, Error **errp)
+{
+    const char *t = qemu_opt_get(opts, "thread");
+    if (t) {
+        if (strcmp(t, "multi") == 0) {
+            mttcg_enabled = true;
+        } else if (strcmp(t, "single") == 0) {
+            mttcg_enabled = false;
+        } else {
+            error_setg(errp, "Invalid 'thread' setting %s", t);
+        }
+    } else {
+        mttcg_enabled = default_mttcg_enabled();
+    }
+}
 
 int64_t cpu_get_icount_raw(void)
 {
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 8ee770a..682788b 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -390,6 +390,15 @@ extern struct CPUTailQ cpus;
 extern __thread CPUState *current_cpu;
 
 /**
+ * qemu_tcg_mttcg_enabled:
+ * Check whether we are running MultiThread TCG or not.
+ *
+ * Returns: %true if we are in MTTCG mode %false otherwise.
+ */
+extern bool mttcg_enabled;
+#define qemu_tcg_mttcg_enabled() (mttcg_enabled)
+
+/**
  * 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 fe992a8..c5055f9 100644
--- a/include/sysemu/cpus.h
+++ b/include/sysemu/cpus.h
@@ -39,4 +39,6 @@ extern int smp_threads;
 
 void list_cpus(FILE *f, fprintf_function cpu_fprintf, const char *optarg);
 
+void qemu_tcg_configure(QemuOpts *opts, Error **errp);
+
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index 8e0d9a5..aa27b54 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -96,6 +96,26 @@ STEXI
 Select CPU model (@code{-cpu help} for list and additional feature selection)
 ETEXI
 
+DEF("accel", HAS_ARG, QEMU_OPTION_accel,
+    "-accel [accel=]accelerator[,thread=single|multi]\n"
+    "               select accelerator ('-accel help for list')\n"
+    "               thread=single|multi (enable multi-threaded TCG)", QEMU_ARCH_ALL)
+STEXI
+@item -accel @var{name}[,prop=@var{value}[,...]]
+@findex -accel
+This is used to enable an accelerator. Depending on the target architecture,
+kvm, xen, or tcg can be available. By default, tcg is used. If there is more
+than one accelerator specified, the next one is used if the previous one fails
+to initialize.
+@table @option
+@item thread=single|multi
+Controls number of TCG threads. When the TCG is multi-threaded there will be one
+thread per vCPU therefor taking advantage of additional host cores. The default
+is to enable multi-threading where both the back-end and front-ends support it and
+no incompatible TCG features have been enabled (e.g. icount/replay).
+@end table
+ETEXI
+
 DEF("smp", HAS_ARG, QEMU_OPTION_smp,
     "-smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,sockets=sockets]\n"
     "                set the number of CPUs to 'n' [default=1]\n"
diff --git a/vl.c b/vl.c
index a455947..eeeea08 100644
--- a/vl.c
+++ b/vl.c
@@ -293,6 +293,26 @@ static QemuOptsList qemu_machine_opts = {
     },
 };
 
+static QemuOptsList qemu_accel_opts = {
+    .name = "accel",
+    .implied_opt_name = "accel",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_accel_opts.head),
+    .merge_lists = true,
+    .desc = {
+        {
+            .name = "accel",
+            .type = QEMU_OPT_STRING,
+            .help = "Select the type of accelerator",
+        },
+        {
+            .name = "thread",
+            .type = QEMU_OPT_STRING,
+            .help = "Enable/disable multi-threaded TCG",
+        },
+        { /* end of list */ }
+    },
+};
+
 static QemuOptsList qemu_boot_opts = {
     .name = "boot-opts",
     .implied_opt_name = "order",
@@ -2936,7 +2956,8 @@ 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;
     QemuOptsList *olist;
     int optind;
     const char *optarg;
@@ -2986,6 +3007,7 @@ int main(int argc, char **argv, char **envp)
     qemu_add_opts(&qemu_trace_opts);
     qemu_add_opts(&qemu_option_rom_opts);
     qemu_add_opts(&qemu_machine_opts);
+    qemu_add_opts(&qemu_accel_opts);
     qemu_add_opts(&qemu_mem_opts);
     qemu_add_opts(&qemu_smp_opts);
     qemu_add_opts(&qemu_boot_opts);
@@ -3676,6 +3698,27 @@ int main(int argc, char **argv, char **envp)
                 qdev_prop_register_global(&kvm_pit_lost_tick_policy);
                 break;
             }
+            case QEMU_OPTION_accel:
+                opts = qemu_opts_parse_noisily(qemu_find_opts("accel"),
+                                               optarg, true);
+                optarg = qemu_opt_get(opts, "accel");
+
+                olist = qemu_find_opts("machine");
+                if (strcmp("kvm", optarg) == 0) {
+                    qemu_opts_parse_noisily(olist, "accel=kvm", false);
+                } else if (strcmp("xen", optarg) == 0) {
+                    qemu_opts_parse_noisily(olist, "accel=xen", false);
+                } else if (strcmp("tcg", optarg) == 0) {
+                    qemu_opts_parse_noisily(olist, "accel=tcg", false);
+                    qemu_tcg_configure(opts, &error_fatal);
+                } else {
+                    if (!is_help_option(optarg)) {
+                        error_printf("Unknown accelerator: %s", optarg);
+                    }
+                    error_printf("Supported accelerators: kvm, xen, tcg\n");
+                    exit(1);
+                }
+                break;
             case QEMU_OPTION_usb:
                 olist = qemu_find_opts("machine");
                 qemu_opts_parse_noisily(olist, "usb=on", false);
@@ -4340,6 +4383,9 @@ int main(int argc, char **argv, char **envp)
         if (kvm_enabled() || xen_enabled()) {
             error_report("-icount is not allowed with kvm or xen");
             exit(1);
+        } else if (qemu_tcg_mttcg_enabled()) {
+            error_report("-icount does not currently work with MTTCG");
+            exit(1);
         }
         configure_icount(icount_opts, &error_abort);
         qemu_opts_del(icount_opts);
-- 
2.7.4