On 08/11/2019 16:34, Laurent Vivier wrote: > On 08/11/2019 15:26, David Gibson wrote: >> On Fri, Nov 08, 2019 at 02:11:03PM +0100, Laurent Vivier wrote: >>> On 24/10/2019 10:17, David Gibson wrote: >>>> From: Greg Kurz <gr...@kaod.org> >>>> >>>> Support for setting VSMT is available in KVM since linux-4.13. Most distros >>>> that support KVM on POWER already have it. It thus seem reasonable enough >>>> to have the default machine to set VSMT to smp_threads. >>>> >>>> This brings contiguous VCPU ids and thus brings their upper bound down to >>>> the machine's max_cpus. This is especially useful for XIVE KVM devices, >>>> which may thus allocate only one VP descriptor per VCPU. >>>> >>>> Signed-off-by: Greg Kurz <gr...@kaod.org> >>>> Message-Id: <157010411885.246126.12610015369068227139.st...@bahia.lan> >>>> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> >>>> --- >>>> hw/ppc/spapr.c | 7 ++++++- >>>> include/hw/ppc/spapr.h | 1 + >>>> 2 files changed, 7 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c >>>> index 4eb97d3a9b..428b834f30 100644 >>>> --- a/hw/ppc/spapr.c >>>> +++ b/hw/ppc/spapr.c >>>> @@ -2496,6 +2496,7 @@ static CPUArchId *spapr_find_cpu_slot(MachineState >>>> *ms, uint32_t id, int *idx) >>>> static void spapr_set_vsmt_mode(SpaprMachineState *spapr, Error **errp) >>>> { >>>> MachineState *ms = MACHINE(spapr); >>>> + SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(spapr); >>>> Error *local_err = NULL; >>>> bool vsmt_user = !!spapr->vsmt; >>>> int kvm_smt = kvmppc_smt_threads(); >>>> @@ -2522,7 +2523,7 @@ static void spapr_set_vsmt_mode(SpaprMachineState >>>> *spapr, Error **errp) >>>> goto out; >>>> } >>>> /* In this case, spapr->vsmt has been set by the command line */ >>>> - } else { >>>> + } else if (!smc->smp_threads_vsmt) { >>>> /* >>>> * Default VSMT value is tricky, because we need it to be as >>>> * consistent as possible (for migration), but this requires >>>> @@ -2531,6 +2532,8 @@ static void spapr_set_vsmt_mode(SpaprMachineState >>>> *spapr, Error **errp) >>>> * overwhelmingly common case in production systems. >>>> */ >>>> spapr->vsmt = MAX(8, smp_threads); >>>> + } else { >>>> + spapr->vsmt = smp_threads; >>>> } >>>> >>>> /* KVM: If necessary, set the SMT mode: */ >>>> @@ -4438,6 +4441,7 @@ static void spapr_machine_class_init(ObjectClass >>>> *oc, void *data) >>>> smc->irq = &spapr_irq_dual; >>>> smc->dr_phb_enabled = true; >>>> smc->linux_pci_probe = true; >>>> + smc->smp_threads_vsmt = true; >>>> } >>>> >>>> static const TypeInfo spapr_machine_info = { >>>> @@ -4505,6 +4509,7 @@ static void >>>> spapr_machine_4_1_class_options(MachineClass *mc) >>>> >>>> spapr_machine_4_2_class_options(mc); >>>> smc->linux_pci_probe = false; >>>> + smc->smp_threads_vsmt = false; >>>> compat_props_add(mc->compat_props, hw_compat_4_1, hw_compat_4_1_len); >>>> compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat)); >>>> } >>>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h >>>> index cbd1a4c9f3..2009eb64f9 100644 >>>> --- a/include/hw/ppc/spapr.h >>>> +++ b/include/hw/ppc/spapr.h >>>> @@ -122,6 +122,7 @@ struct SpaprMachineClass { >>>> bool broken_host_serial_model; /* present real host info to the guest >>>> */ >>>> bool pre_4_1_migration; /* don't migrate hpt-max-page-size */ >>>> bool linux_pci_probe; >>>> + bool smp_threads_vsmt; /* set VSMT to smp_threads by default */ >>>> >>>> void (*phb_placement)(SpaprMachineState *spapr, uint32_t index, >>>> uint64_t *buid, hwaddr *pio, >>>> >>> >>> This patch breaks tests/migration-test on P8 host with kernel older than >>> 4.3 because it tries by default to set the VSMT to 1. >>> >>> qemu-system-ppc64: Failed to set KVM's VSMT mode to 1 (errno -22) >>> On PPC, a VM with 1 threads/core on a host with 8 threads/core requires >>> the use of VSMT mode 1. >>> This KVM seems to be too old to support VSMT. >>> >>> As this is clearly intentional, is there a way to fix migration-test? >> >> Hrm. I believe the argument for this was that the broken kernels were >> old enough we didn't care. What platform are you testing on where >> you're hitting this? >> > > I'm going to propose a patch to fix this problem. > (it was on RHEL7)
Patch sent: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel Message-Id: <20191108154035.12913-1-lviv...@redhat.com> Thanks, Laurent