[Qemu-devel] [PATCH] spapr: ensure we have at least one XICS server

[Qemu-devel] [PATCH] spapr: ensure we have at least one XICS server

[Greg Kurz]

XICS needs to know the upper value for cpu_index as it is used to compute
the number of servers:

    smp_cpus * kvmppc_smt_threads() / smp_threads

When passing -smp cpus=1,threads=9 on a POWER8 host, we end up with:

    1 * 8 / 9 = 0

... which leads to an assertion in both emulated:

Number of servers needs to be greater 0
Aborted (core dumped)

... and in-kernel XICS:

xics_kvm_realize: Assertion `icp->nr_servers' failed.
Aborted (core dumped)

With this patch, we are sure that nr_servers > 0. Passing the same bogus
-smp option then leads to:

qemu-system-ppc64: Cannot support more than 8 threads on PPC with KVM

... which is a lot more explicit than the XICS errors.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
 hw/ppc/spapr.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 35dca77..92916df 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1475,7 +1475,8 @@ static void ppc_spapr_init(MachineState *machine)
 
     /* Set up Interrupt Controller before we create the VCPUs */
     spapr->icp = xics_system_init(machine,
-                                  smp_cpus * kvmppc_smt_threads() / smp_threads,
+                                  DIV_ROUND_UP(smp_cpus * kvmppc_smt_threads(),
+                                               smp_threads),
                                   XICS_IRQS);
 
     /* init CPUs */

Re: [Qemu-devel] [PATCH] spapr: ensure we have at least one XICS server

[David Gibson]

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On Wed, May 13, 2015 at 12:29:33PM +0200, Greg Kurz wrote:
> XICS needs to know the upper value for cpu_index as it is used to compute
> the number of servers:
> 
>     smp_cpus * kvmppc_smt_threads() / smp_threads
> 
> When passing -smp cpus=1,threads=9 on a POWER8 host, we end up with:
> 
>     1 * 8 / 9 = 0
> 
> ... which leads to an assertion in both emulated:
> 
> Number of servers needs to be greater 0
> Aborted (core dumped)
> 
> ... and in-kernel XICS:
> 
> xics_kvm_realize: Assertion `icp->nr_servers' failed.
> Aborted (core dumped)
> 
> With this patch, we are sure that nr_servers > 0. Passing the same bogus
> -smp option then leads to:
> 
> qemu-system-ppc64: Cannot support more than 8 threads on PPC with KVM
> 
> ... which is a lot more explicit than the XICS errors.
> 
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>

Looks sensible, thanks.

Applied to spapr-next branch.

-- 
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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