Re: [Xen-devel] [PATCH 3/3] xen: support runqueue steal time on xen
On 05/07/16 17:23, Stefano Stabellini wrote: > On Wed, 22 Jun 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 >> --- >> drivers/xen/time.c | 42 +- >> 1 file changed, 25 insertions(+), 17 deletions(-) >> >> diff --git a/drivers/xen/time.c b/drivers/xen/time.c >> index 2257b66..65afbe9 100644 >> --- a/drivers/xen/time.c >> +++ b/drivers/xen/time.c >> @@ -19,6 +19,9 @@ >> /* runstate info updated by Xen */ >> static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate); >> >> +/* runstate info of remote cpu accessible */ >> +static bool xen_runstate_remote; > > Honestly I would rather have one global variable less if it means only > dropping one BUG_ON. Okay, I'll remove it. Juergen ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH 3/3] xen: support runqueue steal time on xen
On Wed, 22 Jun 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
> ---
> drivers/xen/time.c | 42 +-
> 1 file changed, 25 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/xen/time.c b/drivers/xen/time.c
> index 2257b66..65afbe9 100644
> --- a/drivers/xen/time.c
> +++ b/drivers/xen/time.c
> @@ -19,6 +19,9 @@
> /* runstate info updated by Xen */
> static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
>
> +/* runstate info of remote cpu accessible */
> +static bool xen_runstate_remote;
Honestly I would rather have one global variable less if it means only
dropping one BUG_ON.
> /* return an consistent snapshot of 64-bit time/counter value */
> static u64 get64(const u64 *p)
> {
> @@ -47,27 +50,31 @@ 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 +87,8 @@ static u64 xen_steal_clock(int cpu)
> {
> struct vcpu_runstate_info state;
>
> - BUG_ON(cpu != smp_processor_id());
> - xen_get_runstate_snapshot(&state);
> + BUG_ON(!xen_runstate_remote && cpu != smp_processor_id());
> + xen_get_runstate_snapshot_cpu(&state, cpu);
> return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> }
>
> @@ -98,11 +105,12 @@ void xen_setup_runstate_info(int cpu)
>
> void __init xen_time_setup_guest(void)
> {
> + 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(¶virt_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(¶virt_steal_rq_enabled);
> }
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[Xen-devel] [PATCH 3/3] xen: support runqueue steal time on xen
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
---
drivers/xen/time.c | 42 +-
1 file changed, 25 insertions(+), 17 deletions(-)
diff --git a/drivers/xen/time.c b/drivers/xen/time.c
index 2257b66..65afbe9 100644
--- a/drivers/xen/time.c
+++ b/drivers/xen/time.c
@@ -19,6 +19,9 @@
/* runstate info updated by Xen */
static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
+/* runstate info of remote cpu accessible */
+static bool xen_runstate_remote;
+
/* return an consistent snapshot of 64-bit time/counter value */
static u64 get64(const u64 *p)
{
@@ -47,27 +50,31 @@ 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 +87,8 @@ static u64 xen_steal_clock(int cpu)
{
struct vcpu_runstate_info state;
- BUG_ON(cpu != smp_processor_id());
- xen_get_runstate_snapshot(&state);
+ BUG_ON(!xen_runstate_remote && cpu != smp_processor_id());
+ xen_get_runstate_snapshot_cpu(&state, cpu);
return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
}
@@ -98,11 +105,12 @@ void xen_setup_runstate_info(int cpu)
void __init xen_time_setup_guest(void)
{
+ 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(¶virt_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(¶virt_steal_rq_enabled);
}
--
2.6.6
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