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SubjectRe: [PATCH v2 3/3] xen: support runqueue steal time on xen
On Wed, 6 Jul 2016, Juergen Gross wrote:
> Up to now reading the stolen time of a remote cpu was not possible in a
> performant way under Xen. This made support of runqueue steal time via
> paravirt_steal_rq_enabled impossible.
>
> With the addition of an appropriate hypervisor interface this is now
> possible, so add the support.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> V2: removed static variable as requested by Stefano Stabellini
> ---
> drivers/xen/time.c | 40 +++++++++++++++++++++++-----------------
> 1 file changed, 23 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/xen/time.c b/drivers/xen/time.c
> index 2257b66..a7fe35b 100644
> --- a/drivers/xen/time.c
> +++ b/drivers/xen/time.c
> @@ -47,27 +47,31 @@ static u64 get64(const u64 *p)
> return ret;
> }
>
> -/*
> - * Runstate accounting
> - */
> -void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
> +static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
> + unsigned int cpu)
> {
> u64 state_time;
> struct vcpu_runstate_info *state;
>
> BUG_ON(preemptible());
>
> - state = this_cpu_ptr(&xen_runstate);
> + state = per_cpu_ptr(&xen_runstate, cpu);
>
> - /*
> - * The runstate info is always updated by the hypervisor on
> - * the current CPU, so there's no need to use anything
> - * stronger than a compiler barrier when fetching it.
> - */
> do {
> state_time = get64(&state->state_entry_time);
> + rmb(); /* Hypervisor might update data. */
> *res = READ_ONCE(*state);
> - } while (get64(&state->state_entry_time) != state_time);
> + rmb(); /* Hypervisor might update data. */
> + } while (get64(&state->state_entry_time) != state_time ||
> + (state_time & XEN_RUNSTATE_UPDATE));
> +}
> +
> +/*
> + * Runstate accounting
> + */
> +void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
> +{
> + xen_get_runstate_snapshot_cpu(res, smp_processor_id());
> }
>
> /* return true when a vcpu could run but has no real cpu to run on */
> @@ -80,8 +84,7 @@ static u64 xen_steal_clock(int cpu)
> {
> struct vcpu_runstate_info state;
>
> - BUG_ON(cpu != smp_processor_id());
> - xen_get_runstate_snapshot(&state);
> + xen_get_runstate_snapshot_cpu(&state, cpu);
> return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> }
>
> @@ -98,11 +101,14 @@ void xen_setup_runstate_info(int cpu)
>
> void __init xen_time_setup_guest(void)
> {
> + bool xen_runstate_remote;
> +
> + xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable,
> + VMASST_TYPE_runstate_update_flag);
> +
> pv_time_ops.steal_clock = xen_steal_clock;
>
> static_key_slow_inc(&paravirt_steal_enabled);
> - /*
> - * We can't set paravirt_steal_rq_enabled as this would require the
> - * capability to read another cpu's runstate info.
> - */
> + if (xen_runstate_remote)
> + static_key_slow_inc(&paravirt_steal_rq_enabled);
> }
> --
> 2.6.6
>

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