On Wed, 17 Jul 2019 15:39:51 +1000
Nicholas Piggin <npig...@gmail.com> wrote:
> This does not do directed yielding and is not quite as strict as PAPR
> specifies in terms of precise dispatch behaviour. This generally will
> mean suboptimal performance, rather than guest misbehaviour. Linux
> does not rely on exact dispatch behaviour.
>
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> ---
LGTM.
Reviewed-by: Greg Kurz <gr...@kaod.org>
Just two minor comments, see below.
> Changes since v4:
> - Style, added justification comments, spelling.
> - Fixed trying to dereference spapr_cpu for a -1 target.
>
> hw/ppc/spapr_hcall.c | 68 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 68 insertions(+)
>
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 8b208ab259..5e655172b2 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1069,6 +1069,73 @@ static target_ulong h_cede(PowerPCCPU *cpu,
> SpaprMachineState *spapr,
> return H_SUCCESS;
> }
>
> +static target_ulong h_confer(PowerPCCPU *cpu, SpaprMachineState *spapr,
> + target_ulong opcode, target_ulong *args)
> +{
> + target_long target = args[0];
> + uint32_t dispatch = args[1];
> + CPUState *cs = CPU(cpu);
> + SpaprCpuState *spapr_cpu;
> +
> + /*
> + * -1 means confer to all other CPUs without dispatch counter check,
> + * otherwise it's a targeted confer.
> + */
> + if (target != -1) {
> + PowerPCCPU *target_cpu = spapr_find_cpu(target);
> + CPUState *target_cs = CPU(target_cpu);
> + unsigned int target_dispatch;
Maybe make it uint32_t to be consistent with dispatch above, and this
is the actual return type of ldl_be_phys() ?
> +
> + if (!target_cs) {
This is the only user of target_cs, maybe drop it and use target_cpu
instead ?
> + return H_PARAMETER;
> + }
> +
> + spapr_cpu = spapr_cpu_state(target_cpu);
> +
> + /*
> + * target == self is a special case, we wait until prodded, without
> + * dispatch counter check.
> + */
> + if (cpu == target_cpu) {
> + if (spapr_cpu->prod) {
> + spapr_cpu->prod = false;
> +
> + return H_SUCCESS;
> + }
> +
> + cs->halted = 1;
> + cs->exception_index = EXCP_HALTED;
> + cs->exit_request = 1;
> +
> + return H_SUCCESS;
> + }
> +
> + if (!spapr_cpu->vpa_addr || ((dispatch & 1) == 0)) {
> + return H_SUCCESS;
> + }
> +
> + target_dispatch = ldl_be_phys(cs->as,
> + spapr_cpu->vpa_addr +
> VPA_DISPATCH_COUNTER);
> + if (target_dispatch != dispatch) {
> + return H_SUCCESS;
> + }
> +
> + /*
> + * The targeted confer does not do anything special beyond yielding
> + * the current vCPU, but even this should be better than nothing.
> + * At least for single-threaded tcg, it gives the target a chance to
> + * run before we run again. Multi-threaded tcg does not really do
> + * anything with EXCP_YIELD yet.
> + */
> + }
> +
> + cs->exception_index = EXCP_YIELD;
> + cs->exit_request = 1;
> + cpu_loop_exit(cs);
> +
> + return H_SUCCESS;
> +}
> +
> static target_ulong h_prod(PowerPCCPU *cpu, SpaprMachineState *spapr,
> target_ulong opcode, target_ulong *args)
> {
> @@ -1909,6 +1976,7 @@ static void hypercall_register_types(void)
> /* hcall-splpar */
> spapr_register_hypercall(H_REGISTER_VPA, h_register_vpa);
> spapr_register_hypercall(H_CEDE, h_cede);
> + spapr_register_hypercall(H_CONFER, h_confer);
> spapr_register_hypercall(H_PROD, h_prod);
>
> spapr_register_hypercall(H_SIGNAL_SYS_RESET, h_signal_sys_reset);
