[Qemu-devel] [PATCH 2/3] KVM: Use -cpu best as default on x86

[Alexander Graf <agraf@suse.de>]

When running QEMU without -cpu parameter, the user usually wants a sane
default. So far, we're using the qemu64/qemu32 CPU type, which basically
means "the maximum TCG can emulate".

That's a really good default when using TCG, but when running with KVM
we much rather want a default saying "the maximum performance I can get".

Fortunately we just added an option that gives us the best performance
while still staying safe on the testability side of things: -cpu best.
So all we need to do is make -cpu best the default when the user doesn't
explicitly specify a CPU type.

This fixes a lot of subtle breakage in the GNU toolchain (libgmp) which
hicks up on QEMU's non-existent CPU models.

This patch also adds a new pc-1.2 machine type to stay backwards compatible
with older versions of QEMU.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v1 -> v2:

  - rebase

v2 -> v3:

  - fix typo in commit message
---
 hw/pc_piix.c |   34 ++++++++++++++++++++++++++--------
 1 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/hw/pc_piix.c b/hw/pc_piix.c
index 0c0096f..a955bf8 100644
--- a/hw/pc_piix.c
+++ b/hw/pc_piix.c
@@ -127,7 +127,8 @@ static void pc_init1(MemoryRegion *system_memory,
                      const char *initrd_filename,
                      const char *cpu_model,
                      int pci_enabled,
-                     int kvmclock_enabled)
+                     int kvmclock_enabled,
+                     int may_cpu_best)
 {
     int i;
     ram_addr_t below_4g_mem_size, above_4g_mem_size;
@@ -149,6 +150,9 @@ static void pc_init1(MemoryRegion *system_memory,
     MemoryRegion *rom_memory;
     void *fw_cfg = NULL;
 
+    if (!cpu_model && kvm_enabled() && may_cpu_best) {
+        cpu_model = "best";
+    }
     pc_cpus_init(cpu_model);
 
     if (kvmclock_enabled) {
@@ -298,7 +302,21 @@ static void pc_init_pci(ram_addr_t ram_size,
              get_system_io(),
              ram_size, boot_device,
              kernel_filename, kernel_cmdline,
-             initrd_filename, cpu_model, 1, 1);
+             initrd_filename, cpu_model, 1, 1, 1);
+}
+
+static void pc_init_pci_oldcpu(ram_addr_t ram_size,
+                               const char *boot_device,
+                               const char *kernel_filename,
+                               const char *kernel_cmdline,
+                               const char *initrd_filename,
+                               const char *cpu_model)
+{
+    pc_init1(get_system_memory(),
+             get_system_io(),
+             ram_size, boot_device,
+             kernel_filename, kernel_cmdline,
+             initrd_filename, cpu_model, 1, 1, 0);
 }
 
 static void pc_init_pci_no_kvmclock(ram_addr_t ram_size,
@@ -312,7 +330,7 @@ static void pc_init_pci_no_kvmclock(ram_addr_t ram_size,
              get_system_io(),
              ram_size, boot_device,
              kernel_filename, kernel_cmdline,
-             initrd_filename, cpu_model, 1, 0);
+             initrd_filename, cpu_model, 1, 0, 0);
 }
 
 static void pc_init_isa(ram_addr_t ram_size,
@@ -328,7 +346,7 @@ static void pc_init_isa(ram_addr_t ram_size,
              get_system_io(),
              ram_size, boot_device,
              kernel_filename, kernel_cmdline,
-             initrd_filename, cpu_model, 0, 1);
+             initrd_filename, cpu_model, 0, 1, 0);
 }
 
 #ifdef CONFIG_XEN
@@ -380,7 +398,7 @@ static QEMUMachine pc_machine_v1_2 = {
 static QEMUMachine pc_machine_v1_1 = {
     .name = "pc-1.1",
     .desc = "Standard PC",
-    .init = pc_init_pci,
+    .init = pc_init_pci_oldcpu,
     .max_cpus = 255,
     .compat_props = (GlobalProperty[]) {
         PC_COMPAT_1_1,
@@ -415,7 +433,7 @@ static QEMUMachine pc_machine_v1_1 = {
 static QEMUMachine pc_machine_v1_0 = {
     .name = "pc-1.0",
     .desc = "Standard PC",
-    .init = pc_init_pci,
+    .init = pc_init_pci_oldcpu,
     .max_cpus = 255,
     .compat_props = (GlobalProperty[]) {
         PC_COMPAT_1_0,
@@ -430,7 +448,7 @@ static QEMUMachine pc_machine_v1_0 = {
 static QEMUMachine pc_machine_v0_15 = {
     .name = "pc-0.15",
     .desc = "Standard PC",
-    .init = pc_init_pci,
+    .init = pc_init_pci_oldcpu,
     .max_cpus = 255,
     .compat_props = (GlobalProperty[]) {
         PC_COMPAT_0_15,
@@ -462,7 +480,7 @@ static QEMUMachine pc_machine_v0_15 = {
 static QEMUMachine pc_machine_v0_14 = {
     .name = "pc-0.14",
     .desc = "Standard PC",
-    .init = pc_init_pci,
+    .init = pc_init_pci_oldcpu,
     .max_cpus = 255,
     .compat_props = (GlobalProperty[]) {
         PC_COMPAT_0_14, 
-- 
1.6.0.2