[Qemu-devel] [PATCH qemu] spapr: Use QEMU limit for maximum CPUs number

[Qemu-devel] [PATCH qemu] spapr: Use QEMU limit for maximum CPUs number

[Alexey Kardashevskiy]

sPAPR uses hard coded limit of maximum 255 supported CPUs which is
exactly the same as QEMU-wide limit which is MAX_CPUMASK_BITS and also
defined as 255.

This makes use of a global CPU number limit for the "pseries" machine.

In order to anticipate future increase of the MAX_CPUMASK_BITS
(or to help debugging large systems), this also bumps the FDT_MAX_SIZE
limit from 256K to 1M assuming that 1 CPU core needs roughly 512 bytes
in the device tree so the new limit can cover up to 2048 CPU cores.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 hw/ppc/spapr.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 6e24bf9..b881459 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -76,7 +76,7 @@
  *
  * We load our kernel at 4M, leaving space for SLOF initial image
  */
-#define FDT_MAX_SIZE            0x40000
+#define FDT_MAX_SIZE            0x100000
 #define RTAS_MAX_SIZE           0x10000
 #define RTAS_MAX_ADDR           0x80000000 /* RTAS must stay below that */
 #define FW_MAX_SIZE             0x400000
@@ -88,8 +88,6 @@
 
 #define TIMEBASE_FREQ           512000000ULL
 
-#define MAX_CPUS                255
-
 #define PHANDLE_XICP            0x00001111
 
 #define HTAB_SIZE(spapr)        (1ULL << ((spapr)->htab_shift))
@@ -2211,7 +2209,7 @@ 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 = MAX_CPUS;
+    mc->max_cpus = MAX_CPUMASK_BITS;
     mc->no_parallel = 1;
     mc->default_boot_order = "";
     mc->default_ram_size = 512 * M_BYTE;
-- 
2.4.0.rc3.8.gfb3e7d5

Re: [Qemu-devel] [PATCH qemu] spapr: Use QEMU limit for maximum CPUs number

[David Gibson]

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On Thu, Aug 06, 2015 at 01:37:24PM +1000, Alexey Kardashevskiy wrote:
> sPAPR uses hard coded limit of maximum 255 supported CPUs which is
> exactly the same as QEMU-wide limit which is MAX_CPUMASK_BITS and also
> defined as 255.
> 
> This makes use of a global CPU number limit for the "pseries" machine.
> 
> In order to anticipate future increase of the MAX_CPUMASK_BITS
> (or to help debugging large systems), this also bumps the FDT_MAX_SIZE
> limit from 256K to 1M assuming that 1 CPU core needs roughly 512 bytes
> in the device tree so the new limit can cover up to 2048 CPU cores.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Applied to spapr-next, thanks.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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