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xen: support runqueue steal time on xen

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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>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
This commit is contained in:
Juergen Gross 2016-07-06 07:00:30 +02:00 committed by David Vrabel
parent 4b5ae0150f
commit 6ba286ad84
1 changed files with 23 additions and 17 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

40
drivers/xen/time.c
View file

@ -47,27 +47,31 @@ static u64 get64(const u64 *p)
return ret; return ret;
} }
/* static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
* Runstate accounting unsigned int cpu)
*/
void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
{ {
u64 state_time; u64 state_time;
struct vcpu_runstate_info *state; struct vcpu_runstate_info *state;
BUG_ON(preemptible()); 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 { do {
state_time = get64(&state->state_entry_time); state_time = get64(&state->state_entry_time);
rmb(); /* Hypervisor might update data. */
*res = READ_ONCE(*state); *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 */ /* 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; struct vcpu_runstate_info state;
BUG_ON(cpu != smp_processor_id()); xen_get_runstate_snapshot_cpu(&state, cpu);
xen_get_runstate_snapshot(&state);
return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; 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) 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; pv_time_ops.steal_clock = xen_steal_clock;
static_key_slow_inc(&paravirt_steal_enabled); static_key_slow_inc(&paravirt_steal_enabled);
/* if (xen_runstate_remote)
* We can't set paravirt_steal_rq_enabled as this would require the static_key_slow_inc(&paravirt_steal_rq_enabled);
* capability to read another cpu's runstate info.
*/
} }