accel: Improve selection of the default accelerator

When compiling with "--disable-tcg", we currently still use "tcg"
as default accelerator. "kvm" should be used in this case instead.
Also, some downstream distros provide QEMU binaries which have "kvm"
in their names (e.g. "qemu-kvm" on RHEL or "kvm" on Ubuntu) that use
KVM by default - and some users might want to do something similar
with upstream binaries, too. Accomodate them by using "kvm:tcg" as
default when we detect such a binary name.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1538748792-19444-1-git-send-email-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 17 insertions, 5 deletions

diff --git a/accel/accel.c b/accel/accel.c
index 6db5d8f4df..68b6d56323 100644
--- a/accel/accel.c
+++ b/accel/accel.c
@@ -69,7 +69,7 @@ static int accel_init_machine(AccelClass *acc, MachineState *ms)
     return ret;
 }
 
-void configure_accelerator(MachineState *ms)
+void configure_accelerator(MachineState *ms, const char *progname)
 {
     const char *accel;
     char **accel_list, **tmp;
@@ -80,8 +80,20 @@ void configure_accelerator(MachineState *ms)
 
     accel = qemu_opt_get(qemu_get_machine_opts(), "accel");
     if (accel == NULL) {
-        /* Use the default "accelerator", tcg */
-        accel = "tcg";
+        /* Select the default accelerator */
+        int pnlen = strlen(progname);
+        if (pnlen >= 3 && g_str_equal(&progname[pnlen - 3], "kvm")) {
+            /* If the program name ends with "kvm", we prefer KVM */
+            accel = "kvm:tcg";
+        } else {
+#if defined(CONFIG_TCG)
+            accel = "tcg";
+#elif defined(CONFIG_KVM)
+            accel = "kvm";
+#else
+#error "No default accelerator available"
+#endif
+        }
     }
 
     accel_list = g_strsplit(accel, ":", 0);
diff --git a/include/sysemu/accel.h b/include/sysemu/accel.h
index f331d128e9..5565e00a96 100644
--- a/include/sysemu/accel.h
+++ b/include/sysemu/accel.h
@@ -66,7 +66,7 @@ typedef struct AccelClass {
 
 extern unsigned long tcg_tb_size;
 
-void configure_accelerator(MachineState *ms);
+void configure_accelerator(MachineState *ms, const char *progname);
 /* Called just before os_setup_post (ie just before drop OS privs) */
 void accel_setup_post(MachineState *ms);
 
diff --git a/vl.c b/vl.c
index 064872cc98..a903619d14 100644
--- a/vl.c
+++ b/vl.c
@@ -4329,7 +4329,7 @@ int main(int argc, char **argv, char **envp)
     qemu_opt_foreach(machine_opts, machine_set_property, current_machine,
                      &error_fatal);
 
-    configure_accelerator(current_machine);
+    configure_accelerator(current_machine, argv[0]);
 
     if (!qtest_enabled() && machine_class->deprecation_reason) {
         error_report("Machine type '%s' is deprecated: %s",