On Fri, May 19, 2017 at 12:32:20PM +0200, Greg Kurz wrote: > For historical reasons, we compute CPU device-tree ids with a non-trivial > logic. This patch consolidate the logic in a single helper to be used > in various places where it is currently open-coded. > > It is okay to get rid of DIV_ROUND_UP() because we're sure that the number > of threads per core in the guest cannot exceed the number of threads per > core in the host.
However, your new logic still gives different answers in some cases.
In particular when max_cpus is not a multiple of smp_threads. Which
is generally a bad idea, but allowed for older machine types for
compatibility. e.g. smp_threads=4, max_cpus=6 smt=8
Old logic:
DIV_ROUND_UP(6 * 8, 4)
= ⌈48 / 4⌉ = 12
New logic gives: ⌊6 / 4⌋ * 8 + (6 % 4)
= 1 * 8 + 2
= 10
In any case the DIV_ROUND_UP() isn't to handle the case where guest
threads-per-core is bigger than host threads-per-core, it's (IIRC) for
the case where guest threads-per-core is not a factor of host
threads-per-core. Again, a bad idea, but I think allowed in some old
cases.
>
> Signed-off-by: Greg Kurz <gr...@kaod.org>
> ---
> hw/ppc/spapr.c | 6 ++----
> target/ppc/cpu.h | 17 +++++++++++++++++
> target/ppc/translate_init.c | 3 +--
> 3 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 75e298b4c6be..1bb05a9a6b07 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -981,7 +981,6 @@ static void *spapr_build_fdt(sPAPRMachineState *spapr,
> void *fdt;
> sPAPRPHBState *phb;
> char *buf;
> - int smt = kvmppc_smt_threads();
>
> fdt = g_malloc0(FDT_MAX_SIZE);
> _FDT((fdt_create_empty_tree(fdt, FDT_MAX_SIZE)));
> @@ -1021,7 +1020,7 @@ static void *spapr_build_fdt(sPAPRMachineState *spapr,
> _FDT(fdt_setprop_cell(fdt, 0, "#size-cells", 2));
>
> /* /interrupt controller */
> - spapr_dt_xics(DIV_ROUND_UP(max_cpus * smt, smp_threads), fdt,
> PHANDLE_XICP);
> + spapr_dt_xics(ppc_cpu_dt_id_from_index(max_cpus), fdt, PHANDLE_XICP);
>
> ret = spapr_populate_memory(spapr, fdt);
> if (ret < 0) {
> @@ -1977,7 +1976,6 @@ static void spapr_init_cpus(sPAPRMachineState *spapr)
> MachineState *machine = MACHINE(spapr);
> MachineClass *mc = MACHINE_GET_CLASS(machine);
> char *type = spapr_get_cpu_core_type(machine->cpu_model);
> - int smt = kvmppc_smt_threads();
> const CPUArchIdList *possible_cpus;
> int boot_cores_nr = smp_cpus / smp_threads;
> int i;
> @@ -2014,7 +2012,7 @@ static void spapr_init_cpus(sPAPRMachineState *spapr)
> sPAPRDRConnector *drc =
> spapr_dr_connector_new(OBJECT(spapr),
> SPAPR_DR_CONNECTOR_TYPE_CPU,
> - (core_id / smp_threads) * smt);
> + ppc_cpu_dt_id_from_index(core_id));
>
> qemu_register_reset(spapr_drc_reset, drc);
> }
> diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
> index 401e10e7dad8..47fe6c64698f 100644
> --- a/target/ppc/cpu.h
> +++ b/target/ppc/cpu.h
> @@ -2529,4 +2529,21 @@ int ppc_get_vcpu_dt_id(PowerPCCPU *cpu);
> PowerPCCPU *ppc_get_vcpu_by_dt_id(int cpu_dt_id);
>
> void ppc_maybe_bswap_register(CPUPPCState *env, uint8_t *mem_buf, int len);
> +
> +#if !defined(CONFIG_USER_ONLY)
> +#include "sysemu/cpus.h"
> +#include "target/ppc/kvm_ppc.h"
> +
> +static inline int ppc_cpu_dt_id_from_index(int cpu_index)
> +{
> + /* POWER HV support has an historical limitation that different threads
> + * on a single core cannot be in different guests at the same time. In
> + * order to allow KVM to assign guest threads to host cores accordingly,
> + * CPU device tree ids are spaced by the number of threads per host
> cores.
> + */
> + return (cpu_index / smp_threads) * kvmppc_smt_threads()
> + + (cpu_index % smp_threads);
> +}
> +#endif
> +
> #endif /* PPC_CPU_H */
> diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c
> index 56a0ab22cfbe..837a9a496a65 100644
> --- a/target/ppc/translate_init.c
> +++ b/target/ppc/translate_init.c
> @@ -9851,8 +9851,7 @@ static void ppc_cpu_realizefn(DeviceState *dev, Error
> **errp)
> }
>
> #if !defined(CONFIG_USER_ONLY)
> - cpu->cpu_dt_id = (cs->cpu_index / smp_threads) * max_smt
> - + (cs->cpu_index % smp_threads);
> + cpu->cpu_dt_id = ppc_cpu_dt_id_from_index(cs->cpu_index);
>
> if (kvm_enabled() && !kvm_vcpu_id_is_valid(cpu->cpu_dt_id)) {
> error_setg(errp, "Can't create CPU with id %d in KVM",
> cpu->cpu_dt_id);
>
--
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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