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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

From: Greg Kurz <gkurz@linux.vnet.ibm.com>

Some systems can already provide more than 255 hardware threads.

Bumping the QEMU limit to 1024 seems reasonable:
- it has no visible overhead in top;
- the limit itself has no effect on hot paths.

Cc: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---

With ulimit -u/-n bumped (nproc and nofile), I was able to boot a guest
with 1024 CPUs, both with threads=1 and threads=8.

It takes time though - 3:15 to get to the guest shell but it is probably
expected on 160-threads machine.

---
 hw/ppc/spapr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index e465d7ac98..46b81a625d 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2712,7 +2712,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
     mc->init = ppc_spapr_init;
     mc->reset = ppc_spapr_reset;
     mc->block_default_type = IF_SCSI;
-    mc->max_cpus = 255;
+    mc->max_cpus = 1024;
     mc->no_parallel = 1;
     mc->default_boot_order = "";
     mc->default_ram_size = 512 * M_BYTE;
-- 
2.11.0