[Qemu-devel] [PATCH v2] sysemu: support up to 1024 vCPUs

[Greg Kurz]

Some PowerPC systems can already provide more than 255 hardware threads.
Igor also posted a patch recently, to increase the the maxcpus limit to
288 for x86 targets.

This patch bumps the limit to 1024:
- 1024 is already the limit for PowerPC KVM in several distros
- it has no visible overhead in top
- the limit itself has no effect on hot paths

We only do that for pseries at the moment and keep a 255 limit for the
ARM Virtual Machine.

Signed-off-by: Greg Kurz <address@hidden>
---
v2: - updated changelog
    - keep 255 limit in hw/arm/virt.c
---
 hw/arm/virt.c           |    2 +-
 include/sysemu/sysemu.h |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 56d35c7716e7..438e09c7a57d 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1358,7 +1358,7 @@ static void virt_machine_class_init(ObjectClass *oc, void 
*data)
      * it later in machvirt_init, where we have more information about the
      * configuration of the particular instance.
      */
-    mc->max_cpus = MAX_CPUMASK_BITS;
+    mc->max_cpus = 255;
     mc->has_dynamic_sysbus = true;
     mc->block_default_type = IF_VIRTIO;
     mc->no_cdrom = 1;
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 38fb3cad35e1..89d742caa477 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -185,7 +185,7 @@ extern int mem_prealloc;
  *
  * Note that cpu->get_arch_id() may be larger than MAX_CPUMASK_BITS.
  */
-#define MAX_CPUMASK_BITS 255
+#define MAX_CPUMASK_BITS 1024
 
 #define MAX_OPTION_ROMS 16
 typedef struct QEMUOptionRom {