On Fri, 8 Nov 2019 16:40:35 +0100
Laurent Vivier <lviv...@redhat.com> wrote:
> Commit 29cb4187497d sets by default the VSMT to smp_threads,
> but older kernels (< 4.13) don't support that.
>
> We can reasonably restore previous behavior with this kernel
> to allow to run QEMU as before.
>
> If VSMT is not supported, VSMT will be set to MAX(8, smp_threads)
> as it is done for previous machine types (< pseries-4.2)
>
It is usually _bad_ to base the machine behavior on host capabilities.
What happens if we migrate between an older kernel and a recent one ?
I understand this is to fix tests/migration-test on older kernels.
Couldn't this be achieved with migration-test doing some introspection
and maybe pass vsmt=8 on the QEMU command line ?
> Fixes: 29cb4187497d ("spapr: Set VSMT to smp_threads by default")
> Cc: gr...@kaod.org
> Reported-by: Lukáš Doktor <ldok...@redhat.com>
> Signed-off-by: Laurent Vivier <lviv...@redhat.com>
> ---
> hw/ppc/spapr.c | 2 +-
> target/ppc/kvm.c | 5 +++++
> target/ppc/kvm_ppc.h | 6 ++++++
> 3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 94f9d27096af..f6c8ad1eda32 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2522,7 +2522,7 @@ 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 if (!smc->smp_threads_vsmt) {
> + } else if (!smc->smp_threads_vsmt || !kvmppc_check_smt_possible()) {
> /*
> * Default VSMT value is tricky, because we need it to be as
> * consistent as possible (for migration), but this requires
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 7d2e8969ac5f..40ed59881167 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2060,6 +2060,11 @@ void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int
> mpic_proxy)
> }
> }
>
> +bool kvmppc_check_smt_possible(void)
> +{
> + return kvm_enabled() && cap_ppc_smt_possible;
> +}
> +
> int kvmppc_smt_threads(void)
> {
> return cap_ppc_smt ? cap_ppc_smt : 1;
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index 98bd7d5da6d6..c9629a416b0b 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -27,6 +27,7 @@ void kvmppc_enable_h_page_init(void);
> void kvmppc_set_papr(PowerPCCPU *cpu);
> int kvmppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr);
> void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy);
> +bool kvmppc_check_smt_possible(void);
> int kvmppc_smt_threads(void);
> void kvmppc_hint_smt_possible(Error **errp);
> int kvmppc_set_smt_threads(int smt);
> @@ -159,6 +160,11 @@ static inline void kvmppc_set_mpic_proxy(PowerPCCPU
> *cpu, int mpic_proxy)
> {
> }
>
> +static inline bool kvmppc_check_smt_possible(void)
> +{
> + return false;
> +}
> +
> static inline int kvmppc_smt_threads(void)
> {
> return 1;
