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Subject[PATCH v2 3/3] xen: support runqueue steal time on xen
Date
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>
---
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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