[PATCH v3 0/4] xen/arm: CONFIG_PARAVIRT and stolen ticks accounting

[PATCH v3 0/4] xen/arm: CONFIG_PARAVIRT and stolen ticks accounting

[Stefano Stabellini]

Hi all,
this patch series introduces stolen ticks accounting for Xen on ARM.
Stolen ticks are clocksource ticks that have been "stolen" from the cpu,
typically because Linux is running in a virtual machine and the vcpu has
been descheduled.
To account for these ticks we introduce CONFIG_PARAVIRT and pv_time_ops
so that we can make use of:

kernel/sched/cputime.c:steal_account_process_tick



Stefano Stabellini (4):
      xen: move xen_setup_runstate_info and get_runstate_snapshot to drivers/xen/time.c
      kernel: missing include in cputime.c
      arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops
      xen/arm: account for stolen ticks

 arch/arm/Kconfig                |   20 +++++++++
 arch/arm/include/asm/paravirt.h |   19 ++++++++
 arch/arm/kernel/Makefile        |    1 +
 arch/arm/kernel/paravirt.c      |   25 +++++++++++
 arch/arm/xen/enlighten.c        |   22 +++++++++
 arch/ia64/xen/time.c            |   48 +++------------------
 arch/x86/xen/time.c             |   76 +--------------------------------
 drivers/xen/Makefile            |    2 +-
 drivers/xen/time.c              |   91 +++++++++++++++++++++++++++++++++++++++
 include/xen/xen-ops.h           |    5 ++
 kernel/sched/cputime.c          |    1 +
 11 files changed, 192 insertions(+), 118 deletions(-)
 create mode 100644 arch/arm/include/asm/paravirt.h
 create mode 100644 arch/arm/kernel/paravirt.c
 create mode 100644 drivers/xen/time.c


git://git.kernel.org/pub/scm/linux/kernel/git/sstabellini/xen.git lost_ticks_3

Cheers,

Stefano

[PATCH v3 1/4] xen: move xen_setup_runstate_info and get_runstate_snapshot to drivers/xen/time.c

[Stefano Stabellini]

Changes in v2:
- leave do_stolen_accounting in arch/x86/xen/time.c;
- use the new common functions in arch/ia64/xen/time.c.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
CC: konrad.wilk@oracle.com
---
 arch/ia64/xen/time.c  |   48 +++----------------------
 arch/x86/xen/time.c   |   76 +----------------------------------------
 drivers/xen/Makefile  |    2 +-
 drivers/xen/time.c    |   91 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/xen/xen-ops.h |    5 +++
 5 files changed, 104 insertions(+), 118 deletions(-)
 create mode 100644 drivers/xen/time.c

diff --git a/arch/ia64/xen/time.c b/arch/ia64/xen/time.c
index 1f8244a..79a0b8c 100644
--- a/arch/ia64/xen/time.c
+++ b/arch/ia64/xen/time.c
@@ -34,53 +34,17 @@
 
 #include "../kernel/fsyscall_gtod_data.h"
 
-static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
 static DEFINE_PER_CPU(unsigned long, xen_stolen_time);
 static DEFINE_PER_CPU(unsigned long, xen_blocked_time);
 
 /* taken from i386/kernel/time-xen.c */
 static void xen_init_missing_ticks_accounting(int cpu)
 {
-	struct vcpu_register_runstate_memory_area area;
-	struct vcpu_runstate_info *runstate = &per_cpu(xen_runstate, cpu);
-	int rc;
+	xen_setup_runstate_info(&runstate);
 
-	memset(runstate, 0, sizeof(*runstate));
-
-	area.addr.v = runstate;
-	rc = HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area, cpu,
-				&area);
-	WARN_ON(rc && rc != -ENOSYS);
-
-	per_cpu(xen_blocked_time, cpu) = runstate->time[RUNSTATE_blocked];
-	per_cpu(xen_stolen_time, cpu) = runstate->time[RUNSTATE_runnable]
-					    + runstate->time[RUNSTATE_offline];
-}
-
-/*
- * Runstate accounting
- */
-/* stolen from arch/x86/xen/time.c */
-static void get_runstate_snapshot(struct vcpu_runstate_info *res)
-{
-	u64 state_time;
-	struct vcpu_runstate_info *state;
-
-	BUG_ON(preemptible());
-
-	state = &__get_cpu_var(xen_runstate);
-
-	/*
-	 * 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 = state->state_entry_time;
-		rmb();
-		*res = *state;
-		rmb();
-	} while (state->state_entry_time != state_time);
+	per_cpu(xen_blocked_time, cpu) = runstate.time[RUNSTATE_blocked];
+	per_cpu(xen_stolen_time, cpu) = runstate.time[RUNSTATE_runnable]
+					    + runstate.time[RUNSTATE_offline];
 }
 
 #define NS_PER_TICK (1000000000LL/HZ)
@@ -94,7 +58,7 @@ consider_steal_time(unsigned long new_itm)
 	struct vcpu_runstate_info runstate;
 	struct task_struct *p = current;
 
-	get_runstate_snapshot(&runstate);
+	xen_get_runstate_snapshot(&runstate);
 
 	/*
 	 * Check for vcpu migration effect
@@ -202,7 +166,7 @@ static unsigned long long xen_sched_clock(void)
 	 */
 	now = ia64_native_sched_clock();
 
-	get_runstate_snapshot(&runstate);
+	xen_get_runstate_snapshot(&runstate);
 
 	WARN_ON(runstate.state != RUNSTATE_running);
 
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 0296a95..18d0104 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -30,9 +30,6 @@
 #define TIMER_SLOP	100000
 #define NS_PER_TICK	(1000000000LL / HZ)
 
-/* runstate info updated by Xen */
-static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
-
 /* snapshots of runstate info */
 static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);
 
@@ -40,77 +37,6 @@ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);
 static DEFINE_PER_CPU(u64, xen_residual_stolen);
 static DEFINE_PER_CPU(u64, xen_residual_blocked);
 
-/* return an consistent snapshot of 64-bit time/counter value */
-static u64 get64(const u64 *p)
-{
-	u64 ret;
-
-	if (BITS_PER_LONG < 64) {
-		u32 *p32 = (u32 *)p;
-		u32 h, l;
-
-		/*
-		 * Read high then low, and then make sure high is
-		 * still the same; this will only loop if low wraps
-		 * and carries into high.
-		 * XXX some clean way to make this endian-proof?
-		 */
-		do {
-			h = p32[1];
-			barrier();
-			l = p32[0];
-			barrier();
-		} while (p32[1] != h);
-
-		ret = (((u64)h) << 32) | l;
-	} else
-		ret = *p;
-
-	return ret;
-}
-
-/*
- * Runstate accounting
- */
-static void get_runstate_snapshot(struct vcpu_runstate_info *res)
-{
-	u64 state_time;
-	struct vcpu_runstate_info *state;
-
-	BUG_ON(preemptible());
-
-	state = &__get_cpu_var(xen_runstate);
-
-	/*
-	 * 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);
-		barrier();
-		*res = *state;
-		barrier();
-	} while (get64(&state->state_entry_time) != state_time);
-}
-
-/* return true when a vcpu could run but has no real cpu to run on */
-bool xen_vcpu_stolen(int vcpu)
-{
-	return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
-}
-
-void xen_setup_runstate_info(int cpu)
-{
-	struct vcpu_register_runstate_memory_area area;
-
-	area.addr.v = &per_cpu(xen_runstate, cpu);
-
-	if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
-			       cpu, &area))
-		BUG();
-}
-
 static void do_stolen_accounting(void)
 {
 	struct vcpu_runstate_info state;
@@ -118,7 +44,7 @@ static void do_stolen_accounting(void)
 	s64 blocked, runnable, offline, stolen;
 	cputime_t ticks;
 
-	get_runstate_snapshot(&state);
+	xen_get_runstate_snapshot(&state);
 
 	WARN_ON(state.state != RUNSTATE_running);
 
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index eabd0ee..2bf461a 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -3,7 +3,7 @@ obj-y	+= manage.o
 obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
 endif
 obj-$(CONFIG_X86)			+= fallback.o
-obj-y	+= grant-table.o features.o events.o balloon.o
+obj-y	+= grant-table.o features.o events.o balloon.o time.o
 obj-y	+= xenbus/
 
 nostackp := $(call cc-option, -fno-stack-protector)
diff --git a/drivers/xen/time.c b/drivers/xen/time.c
new file mode 100644
index 0000000..c2e39d3
--- /dev/null
+++ b/drivers/xen/time.c
@@ -0,0 +1,91 @@
+/*
+ * Xen stolen ticks accounting.
+ */
+#include <linux/kernel.h>
+#include <linux/kernel_stat.h>
+#include <linux/math64.h>
+#include <linux/gfp.h>
+
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+
+#include <xen/events.h>
+#include <xen/features.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/vcpu.h>
+#include <xen/xen-ops.h>
+
+/* runstate info updated by Xen */
+static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
+
+/* return an consistent snapshot of 64-bit time/counter value */
+static u64 get64(const u64 *p)
+{
+	u64 ret;
+
+	if (BITS_PER_LONG < 64) {
+		u32 *p32 = (u32 *)p;
+		u32 h, l;
+
+		/*
+		 * Read high then low, and then make sure high is
+		 * still the same; this will only loop if low wraps
+		 * and carries into high.
+		 * XXX some clean way to make this endian-proof?
+		 */
+		do {
+			h = p32[1];
+			barrier();
+			l = p32[0];
+			barrier();
+		} while (p32[1] != h);
+
+		ret = (((u64)h) << 32) | l;
+	} else
+		ret = *p;
+
+	return ret;
+}
+
+/*
+ * Runstate accounting
+ */
+void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
+{
+	u64 state_time;
+	struct vcpu_runstate_info *state;
+
+	BUG_ON(preemptible());
+
+	state = &__get_cpu_var(xen_runstate);
+
+	/*
+	 * 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);
+		barrier();
+		*res = *state;
+		barrier();
+	} while (get64(&state->state_entry_time) != state_time);
+}
+
+/* return true when a vcpu could run but has no real cpu to run on */
+bool xen_vcpu_stolen(int vcpu)
+{
+	return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
+}
+
+void xen_setup_runstate_info(int cpu)
+{
+	struct vcpu_register_runstate_memory_area area;
+
+	area.addr.v = &per_cpu(xen_runstate, cpu);
+
+	if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
+			       cpu, &area))
+		BUG();
+}
+
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index d6fe062..4fd4e47 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -3,6 +3,7 @@
 
 #include <linux/percpu.h>
 #include <asm/xen/interface.h>
+#include <xen/interface/vcpu.h>
 
 DECLARE_PER_CPU(struct vcpu_info *, xen_vcpu);
 
@@ -16,6 +17,10 @@ void xen_mm_unpin_all(void);
 void xen_timer_resume(void);
 void xen_arch_resume(void);
 
+bool xen_vcpu_stolen(int vcpu);
+void xen_setup_runstate_info(int cpu);
+void xen_get_runstate_snapshot(struct vcpu_runstate_info *res);
+
 int xen_setup_shutdown_event(void);
 
 extern unsigned long *xen_contiguous_bitmap;
-- 
1.7.2.5

Re: [PATCH v3 1/4] xen: move xen_setup_runstate_info and get_runstate_snapshot to drivers/xen/time.c

[Konrad Rzeszutek Wilk]

On Wed, May 08, 2013 at 04:41:51PM +0100, Stefano Stabellini wrote:
> Changes in v2:
> - leave do_stolen_accounting in arch/x86/xen/time.c;
> - use the new common functions in arch/ia64/xen/time.c.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
> CC: konrad.wilk@oracle.com

On the generic and x86 side it looks OK to me. I presume you did a sanity
check on x86 to make sure nothing was off?

> ---
>  arch/ia64/xen/time.c  |   48 +++----------------------
>  arch/x86/xen/time.c   |   76 +----------------------------------------
>  drivers/xen/Makefile  |    2 +-
>  drivers/xen/time.c    |   91 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/xen/xen-ops.h |    5 +++
>  5 files changed, 104 insertions(+), 118 deletions(-)
>  create mode 100644 drivers/xen/time.c
> 
> diff --git a/arch/ia64/xen/time.c b/arch/ia64/xen/time.c
> index 1f8244a..79a0b8c 100644
> --- a/arch/ia64/xen/time.c
> +++ b/arch/ia64/xen/time.c
> @@ -34,53 +34,17 @@
>  
>  #include "../kernel/fsyscall_gtod_data.h"
>  
> -static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
>  static DEFINE_PER_CPU(unsigned long, xen_stolen_time);
>  static DEFINE_PER_CPU(unsigned long, xen_blocked_time);
>  
>  /* taken from i386/kernel/time-xen.c */
>  static void xen_init_missing_ticks_accounting(int cpu)
>  {
> -	struct vcpu_register_runstate_memory_area area;
> -	struct vcpu_runstate_info *runstate = &per_cpu(xen_runstate, cpu);
> -	int rc;
> +	xen_setup_runstate_info(&runstate);
>  
> -	memset(runstate, 0, sizeof(*runstate));
> -
> -	area.addr.v = runstate;
> -	rc = HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area, cpu,
> -				&area);
> -	WARN_ON(rc && rc != -ENOSYS);
> -
> -	per_cpu(xen_blocked_time, cpu) = runstate->time[RUNSTATE_blocked];
> -	per_cpu(xen_stolen_time, cpu) = runstate->time[RUNSTATE_runnable]
> -					    + runstate->time[RUNSTATE_offline];
> -}
> -
> -/*
> - * Runstate accounting
> - */
> -/* stolen from arch/x86/xen/time.c */
> -static void get_runstate_snapshot(struct vcpu_runstate_info *res)
> -{
> -	u64 state_time;
> -	struct vcpu_runstate_info *state;
> -
> -	BUG_ON(preemptible());
> -
> -	state = &__get_cpu_var(xen_runstate);
> -
> -	/*
> -	 * 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 = state->state_entry_time;
> -		rmb();
> -		*res = *state;
> -		rmb();
> -	} while (state->state_entry_time != state_time);
> +	per_cpu(xen_blocked_time, cpu) = runstate.time[RUNSTATE_blocked];
> +	per_cpu(xen_stolen_time, cpu) = runstate.time[RUNSTATE_runnable]
> +					    + runstate.time[RUNSTATE_offline];
>  }
>  
>  #define NS_PER_TICK (1000000000LL/HZ)
> @@ -94,7 +58,7 @@ consider_steal_time(unsigned long new_itm)
>  	struct vcpu_runstate_info runstate;
>  	struct task_struct *p = current;
>  
> -	get_runstate_snapshot(&runstate);
> +	xen_get_runstate_snapshot(&runstate);
>  
>  	/*
>  	 * Check for vcpu migration effect
> @@ -202,7 +166,7 @@ static unsigned long long xen_sched_clock(void)
>  	 */
>  	now = ia64_native_sched_clock();
>  
> -	get_runstate_snapshot(&runstate);
> +	xen_get_runstate_snapshot(&runstate);
>  
>  	WARN_ON(runstate.state != RUNSTATE_running);
>  
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 0296a95..18d0104 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -30,9 +30,6 @@
>  #define TIMER_SLOP	100000
>  #define NS_PER_TICK	(1000000000LL / HZ)
>  
> -/* runstate info updated by Xen */
> -static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
> -
>  /* snapshots of runstate info */
>  static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);
>  
> @@ -40,77 +37,6 @@ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);
>  static DEFINE_PER_CPU(u64, xen_residual_stolen);
>  static DEFINE_PER_CPU(u64, xen_residual_blocked);
>  
> -/* return an consistent snapshot of 64-bit time/counter value */
> -static u64 get64(const u64 *p)
> -{
> -	u64 ret;
> -
> -	if (BITS_PER_LONG < 64) {
> -		u32 *p32 = (u32 *)p;
> -		u32 h, l;
> -
> -		/*
> -		 * Read high then low, and then make sure high is
> -		 * still the same; this will only loop if low wraps
> -		 * and carries into high.
> -		 * XXX some clean way to make this endian-proof?
> -		 */
> -		do {
> -			h = p32[1];
> -			barrier();
> -			l = p32[0];
> -			barrier();
> -		} while (p32[1] != h);
> -
> -		ret = (((u64)h) << 32) | l;
> -	} else
> -		ret = *p;
> -
> -	return ret;
> -}
> -
> -/*
> - * Runstate accounting
> - */
> -static void get_runstate_snapshot(struct vcpu_runstate_info *res)
> -{
> -	u64 state_time;
> -	struct vcpu_runstate_info *state;
> -
> -	BUG_ON(preemptible());
> -
> -	state = &__get_cpu_var(xen_runstate);
> -
> -	/*
> -	 * 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);
> -		barrier();
> -		*res = *state;
> -		barrier();
> -	} while (get64(&state->state_entry_time) != state_time);
> -}
> -
> -/* return true when a vcpu could run but has no real cpu to run on */
> -bool xen_vcpu_stolen(int vcpu)
> -{
> -	return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
> -}
> -
> -void xen_setup_runstate_info(int cpu)
> -{
> -	struct vcpu_register_runstate_memory_area area;
> -
> -	area.addr.v = &per_cpu(xen_runstate, cpu);
> -
> -	if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
> -			       cpu, &area))
> -		BUG();
> -}
> -
>  static void do_stolen_accounting(void)
>  {
>  	struct vcpu_runstate_info state;
> @@ -118,7 +44,7 @@ static void do_stolen_accounting(void)
>  	s64 blocked, runnable, offline, stolen;
>  	cputime_t ticks;
>  
> -	get_runstate_snapshot(&state);
> +	xen_get_runstate_snapshot(&state);
>  
>  	WARN_ON(state.state != RUNSTATE_running);
>  
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index eabd0ee..2bf461a 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -3,7 +3,7 @@ obj-y	+= manage.o
>  obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
>  endif
>  obj-$(CONFIG_X86)			+= fallback.o
> -obj-y	+= grant-table.o features.o events.o balloon.o
> +obj-y	+= grant-table.o features.o events.o balloon.o time.o
>  obj-y	+= xenbus/
>  
>  nostackp := $(call cc-option, -fno-stack-protector)
> diff --git a/drivers/xen/time.c b/drivers/xen/time.c
> new file mode 100644
> index 0000000..c2e39d3
> --- /dev/null
> +++ b/drivers/xen/time.c
> @@ -0,0 +1,91 @@
> +/*
> + * Xen stolen ticks accounting.
> + */
> +#include <linux/kernel.h>
> +#include <linux/kernel_stat.h>
> +#include <linux/math64.h>
> +#include <linux/gfp.h>
> +
> +#include <asm/xen/hypervisor.h>
> +#include <asm/xen/hypercall.h>
> +
> +#include <xen/events.h>
> +#include <xen/features.h>
> +#include <xen/interface/xen.h>
> +#include <xen/interface/vcpu.h>
> +#include <xen/xen-ops.h>
> +
> +/* runstate info updated by Xen */
> +static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
> +
> +/* return an consistent snapshot of 64-bit time/counter value */
> +static u64 get64(const u64 *p)
> +{
> +	u64 ret;
> +
> +	if (BITS_PER_LONG < 64) {
> +		u32 *p32 = (u32 *)p;
> +		u32 h, l;
> +
> +		/*
> +		 * Read high then low, and then make sure high is
> +		 * still the same; this will only loop if low wraps
> +		 * and carries into high.
> +		 * XXX some clean way to make this endian-proof?
> +		 */
> +		do {
> +			h = p32[1];
> +			barrier();
> +			l = p32[0];
> +			barrier();
> +		} while (p32[1] != h);
> +
> +		ret = (((u64)h) << 32) | l;
> +	} else
> +		ret = *p;
> +
> +	return ret;
> +}
> +
> +/*
> + * Runstate accounting
> + */
> +void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
> +{
> +	u64 state_time;
> +	struct vcpu_runstate_info *state;
> +
> +	BUG_ON(preemptible());
> +
> +	state = &__get_cpu_var(xen_runstate);
> +
> +	/*
> +	 * 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);
> +		barrier();
> +		*res = *state;
> +		barrier();
> +	} while (get64(&state->state_entry_time) != state_time);
> +}
> +
> +/* return true when a vcpu could run but has no real cpu to run on */
> +bool xen_vcpu_stolen(int vcpu)
> +{
> +	return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
> +}
> +
> +void xen_setup_runstate_info(int cpu)
> +{
> +	struct vcpu_register_runstate_memory_area area;
> +
> +	area.addr.v = &per_cpu(xen_runstate, cpu);
> +
> +	if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
> +			       cpu, &area))
> +		BUG();
> +}
> +
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index d6fe062..4fd4e47 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -3,6 +3,7 @@
>  
>  #include <linux/percpu.h>
>  #include <asm/xen/interface.h>
> +#include <xen/interface/vcpu.h>
>  
>  DECLARE_PER_CPU(struct vcpu_info *, xen_vcpu);
>  
> @@ -16,6 +17,10 @@ void xen_mm_unpin_all(void);
>  void xen_timer_resume(void);
>  void xen_arch_resume(void);
>  
> +bool xen_vcpu_stolen(int vcpu);
> +void xen_setup_runstate_info(int cpu);
> +void xen_get_runstate_snapshot(struct vcpu_runstate_info *res);
> +
>  int xen_setup_shutdown_event(void);
>  
>  extern unsigned long *xen_contiguous_bitmap;
> -- 
> 1.7.2.5
> 

Re: [PATCH v3 1/4] xen: move xen_setup_runstate_info and get_runstate_snapshot to drivers/xen/time.c

[Stefano Stabellini]

On Wed, 8 May 2013, Konrad Rzeszutek Wilk wrote:
> On Wed, May 08, 2013 at 04:41:51PM +0100, Stefano Stabellini wrote:
> > Changes in v2:
> > - leave do_stolen_accounting in arch/x86/xen/time.c;
> > - use the new common functions in arch/ia64/xen/time.c.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > Acked-by: Ian Campbell <ian.campbell@citrix.com>
> > CC: konrad.wilk@oracle.com
> 
> On the generic and x86 side it looks OK to me. I presume you did a sanity
> check on x86 to make sure nothing was off?

Yep, it seems to work.
However I couldn't even compile test the ia64 code.

Re: [Xen-devel] [PATCH v3 1/4] xen: move xen_setup_runstate_info and get_runstate_snapshot to drivers/xen/time.c

[Ian Campbell]

On Wed, 2013-05-08 at 19:13 +0100, Stefano Stabellini wrote:
> On Wed, 8 May 2013, Konrad Rzeszutek Wilk wrote:
> > On Wed, May 08, 2013 at 04:41:51PM +0100, Stefano Stabellini wrote:
> > > Changes in v2:
> > > - leave do_stolen_accounting in arch/x86/xen/time.c;
> > > - use the new common functions in arch/ia64/xen/time.c.
> > > 
> > > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > > Acked-by: Ian Campbell <ian.campbell@citrix.com>
> > > CC: konrad.wilk@oracle.com
> > 
> > On the generic and x86 side it looks OK to me. I presume you did a sanity
> > check on x86 to make sure nothing was off?
> 
> Yep, it seems to work.
> However I couldn't even compile test the ia64 code.

The ia64 Xen on Linux support hasn't been touched since circa 2.6.35
AFAIK...

Ian.

[PATCH v3 2/4] kernel: missing include in cputime.c

[Stefano Stabellini]

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: mingo@redhat.com
CC: peterz@infradead.org
---
 kernel/sched/cputime.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index ed12cbb..488a5bf 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -5,6 +5,7 @@
 #include <linux/static_key.h>
 #include <linux/context_tracking.h>
 #include "sched.h"
+#include <asm/paravirt.h>
 
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
-- 
1.7.2.5

[PATCH v3 3/4] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops

[Stefano Stabellini]

Introduce CONFIG_PARAVIRT and PARAVIRT_TIME_ACCOUNTING on ARM.

The only paravirt interface supported is pv_time_ops.steal_clock, so no
runtime pvops patching needed.

This allows us to make use of steal_account_process_tick for stolen
ticks accounting.

Changes in v3:
- improve commit description and Kconfig help text;
- no need to initialize pv_time_ops;
- add PARAVIRT_TIME_ACCOUNTING.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: linux@arm.linux.org.uk
CC: will.deacon@arm.com
CC: nico@linaro.org
CC: marc.zyngier@arm.com
CC: cov@codeaurora.org
CC: arnd@arndb.de
CC: olof@lixom.net
---
 arch/arm/Kconfig                |   20 ++++++++++++++++++++
 arch/arm/include/asm/paravirt.h |   19 +++++++++++++++++++
 arch/arm/kernel/Makefile        |    1 +
 arch/arm/kernel/paravirt.c      |   25 +++++++++++++++++++++++++
 4 files changed, 65 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/include/asm/paravirt.h
 create mode 100644 arch/arm/kernel/paravirt.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 344e299..89ee2f1 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1887,12 +1887,32 @@ config XEN_DOM0
 	def_bool y
 	depends on XEN
 
+config PARAVIRT
+	bool "Enable paravirtualization code"
+	---help---
+	  This changes the kernel so it can modify itself when it is run
+	  under a hypervisor, potentially improving performance significantly
+	  over full virtualization.
+
+config PARAVIRT_TIME_ACCOUNTING
+	bool "Paravirtual steal time accounting"
+	select PARAVIRT
+	default n
+	---help---
+	  Select this option to enable fine granularity task steal time
+	  accounting. Time spent executing other tasks in parallel with
+	  the current vCPU is discounted from the vCPU power. To account for
+	  that, there can be a small performance impact.
+
+	  If in doubt, say N here.
+
 config XEN
 	bool "Xen guest support on ARM (EXPERIMENTAL)"
 	depends on ARM && AEABI && OF
 	depends on CPU_V7 && !CPU_V6
 	depends on !GENERIC_ATOMIC64
 	select ARM_PSCI
+	select PARAVIRT
 	help
 	  Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
 
diff --git a/arch/arm/include/asm/paravirt.h b/arch/arm/include/asm/paravirt.h
new file mode 100644
index 0000000..3b95bc6
--- /dev/null
+++ b/arch/arm/include/asm/paravirt.h
@@ -0,0 +1,19 @@
+#ifndef _ASM_ARM_PARAVIRT_H
+#define _ASM_ARM_PARAVIRT_H
+
+struct static_key;
+extern struct static_key paravirt_steal_enabled;
+extern struct static_key paravirt_steal_rq_enabled;
+
+struct pv_time_ops {
+	unsigned long long (*steal_clock)(int cpu);
+};
+extern struct pv_time_ops pv_time_ops;
+
+static inline u64 paravirt_steal_clock(int cpu)
+{
+	return pv_time_ops.steal_clock(cpu);
+}
+
+
+#endif
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 5f3338e..d911db6 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -76,6 +76,7 @@ obj-$(CONFIG_ARM_CPU_TOPOLOGY)  += topology.o
 ifneq ($(CONFIG_ARCH_EBSA110),y)
   obj-y		+= io.o
 endif
+obj-$(CONFIG_PARAVIRT)	+= paravirt.o
 
 head-y			:= head$(MMUEXT).o
 obj-$(CONFIG_DEBUG_LL)	+= debug.o
diff --git a/arch/arm/kernel/paravirt.c b/arch/arm/kernel/paravirt.c
new file mode 100644
index 0000000..53f371e
--- /dev/null
+++ b/arch/arm/kernel/paravirt.c
@@ -0,0 +1,25 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Copyright (C) 2013 Citrix Systems
+ *
+ * Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
+ */
+
+#include <linux/export.h>
+#include <linux/jump_label.h>
+#include <linux/types.h>
+#include <asm/paravirt.h>
+
+struct static_key paravirt_steal_enabled;
+struct static_key paravirt_steal_rq_enabled;
+
+struct pv_time_ops pv_time_ops;
+EXPORT_SYMBOL_GPL(pv_time_ops);
-- 
1.7.2.5

Re: [PATCH v3 3/4] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops

[Marc Zyngier]

Hi Stefano,

On 08/05/13 16:41, Stefano Stabellini wrote:
> Introduce CONFIG_PARAVIRT and PARAVIRT_TIME_ACCOUNTING on ARM.
> 
> The only paravirt interface supported is pv_time_ops.steal_clock, so no
> runtime pvops patching needed.
> 
> This allows us to make use of steal_account_process_tick for stolen
> ticks accounting.
> 
> Changes in v3:
> - improve commit description and Kconfig help text;
> - no need to initialize pv_time_ops;
> - add PARAVIRT_TIME_ACCOUNTING.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> CC: linux@arm.linux.org.uk
> CC: will.deacon@arm.com
> CC: nico@linaro.org
> CC: marc.zyngier@arm.com
> CC: cov@codeaurora.org
> CC: arnd@arndb.de
> CC: olof@lixom.net
> ---
>  arch/arm/Kconfig                |   20 ++++++++++++++++++++
>  arch/arm/include/asm/paravirt.h |   19 +++++++++++++++++++
>  arch/arm/kernel/Makefile        |    1 +
>  arch/arm/kernel/paravirt.c      |   25 +++++++++++++++++++++++++
>  4 files changed, 65 insertions(+), 0 deletions(-)
>  create mode 100644 arch/arm/include/asm/paravirt.h
>  create mode 100644 arch/arm/kernel/paravirt.c
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 344e299..89ee2f1 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1887,12 +1887,32 @@ config XEN_DOM0
>  	def_bool y
>  	depends on XEN
>  
> +config PARAVIRT
> +	bool "Enable paravirtualization code"
> +	---help---
> +	  This changes the kernel so it can modify itself when it is run
> +	  under a hypervisor, potentially improving performance significantly
> +	  over full virtualization.
> +
> +config PARAVIRT_TIME_ACCOUNTING
> +	bool "Paravirtual steal time accounting"
> +	select PARAVIRT

Surely you meant "depends on" instead of "select" here? Otherwise I
don't really see the point of PARAVIRT...

> +	default n
> +	---help---
> +	  Select this option to enable fine granularity task steal time
> +	  accounting. Time spent executing other tasks in parallel with
> +	  the current vCPU is discounted from the vCPU power. To account for
> +	  that, there can be a small performance impact.
> +
> +	  If in doubt, say N here.
> +
>  config XEN
>  	bool "Xen guest support on ARM (EXPERIMENTAL)"
>  	depends on ARM && AEABI && OF
>  	depends on CPU_V7 && !CPU_V6
>  	depends on !GENERIC_ATOMIC64
>  	select ARM_PSCI
> +	select PARAVIRT
>  	help
>  	  Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
>  
-- 
Jazz is not dead. It just smells funny...

Re: [PATCH v3 3/4] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops

[Stefano Stabellini]

On Wed, 8 May 2013, Marc Zyngier wrote:
> Hi Stefano,
> 
> On 08/05/13 16:41, Stefano Stabellini wrote:
> > Introduce CONFIG_PARAVIRT and PARAVIRT_TIME_ACCOUNTING on ARM.
> > 
> > The only paravirt interface supported is pv_time_ops.steal_clock, so no
> > runtime pvops patching needed.
> > 
> > This allows us to make use of steal_account_process_tick for stolen
> > ticks accounting.
> > 
> > Changes in v3:
> > - improve commit description and Kconfig help text;
> > - no need to initialize pv_time_ops;
> > - add PARAVIRT_TIME_ACCOUNTING.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > CC: linux@arm.linux.org.uk
> > CC: will.deacon@arm.com
> > CC: nico@linaro.org
> > CC: marc.zyngier@arm.com
> > CC: cov@codeaurora.org
> > CC: arnd@arndb.de
> > CC: olof@lixom.net
> > ---
> >  arch/arm/Kconfig                |   20 ++++++++++++++++++++
> >  arch/arm/include/asm/paravirt.h |   19 +++++++++++++++++++
> >  arch/arm/kernel/Makefile        |    1 +
> >  arch/arm/kernel/paravirt.c      |   25 +++++++++++++++++++++++++
> >  4 files changed, 65 insertions(+), 0 deletions(-)
> >  create mode 100644 arch/arm/include/asm/paravirt.h
> >  create mode 100644 arch/arm/kernel/paravirt.c
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index 344e299..89ee2f1 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -1887,12 +1887,32 @@ config XEN_DOM0
> >  	def_bool y
> >  	depends on XEN
> >  
> > +config PARAVIRT
> > +	bool "Enable paravirtualization code"
> > +	---help---
> > +	  This changes the kernel so it can modify itself when it is run
> > +	  under a hypervisor, potentially improving performance significantly
> > +	  over full virtualization.
> > +
> > +config PARAVIRT_TIME_ACCOUNTING
> > +	bool "Paravirtual steal time accounting"
> > +	select PARAVIRT
> 
> Surely you meant "depends on" instead of "select" here? Otherwise I
> don't really see the point of PARAVIRT...

I agree with you that "depends on" seems to be the right thing here, but
on x86 is actually select.

The original commit is 095c0aa83e52d6c3dd7168610746703921f570af.

[PATCH v3 4/4] xen/arm: account for stolen ticks

[Stefano Stabellini]

Register the runstate_memory_area with the hypervisor.
Use pv_time_ops.steal_clock to account for stolen ticks.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Changes in v3:
- use BUG_ON and smp_processor_id.
---
 arch/arm/xen/enlighten.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 13609e0..dfa7738 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -14,7 +14,10 @@
 #include <xen/xen-ops.h>
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
+#include <asm/arch_timer.h>
 #include <asm/system_misc.h>
+#include <asm/paravirt.h>
+#include <linux/jump_label.h>
 #include <linux/interrupt.h>
 #include <linux/irqreturn.h>
 #include <linux/module.h>
@@ -152,6 +155,19 @@ int xen_unmap_domain_mfn_range(struct vm_area_struct *vma,
 }
 EXPORT_SYMBOL_GPL(xen_unmap_domain_mfn_range);
 
+unsigned long long xen_stolen_accounting(int cpu)
+{
+	struct vcpu_runstate_info state;
+
+	BUG_ON(cpu != smp_processor_id());
+
+	xen_get_runstate_snapshot(&state);
+
+	WARN_ON(state.state != RUNSTATE_running);
+
+	return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
+}
+
 static void __init xen_percpu_init(void *unused)
 {
 	struct vcpu_register_vcpu_info info;
@@ -169,6 +185,8 @@ static void __init xen_percpu_init(void *unused)
 	BUG_ON(err);
 	per_cpu(xen_vcpu, cpu) = vcpup;
 
+	xen_setup_runstate_info(cpu);
+
 	enable_percpu_irq(xen_events_irq, 0);
 }
 
@@ -300,6 +318,10 @@ static int __init xen_init_events(void)
 
 	on_each_cpu(xen_percpu_init, NULL, 0);
 
+	pv_time_ops.steal_clock = xen_stolen_accounting;
+	static_key_slow_inc(&paravirt_steal_enabled);
+	static_key_slow_inc(&paravirt_steal_rq_enabled);
+
 	return 0;
 }
 postcore_initcall(xen_init_events);
-- 
1.7.2.5

Re: [PATCH v3 4/4] xen/arm: account for stolen ticks

[Marc Zyngier]

Hi Stefano,

On 08/05/13 16:41, Stefano Stabellini wrote:
> Register the runstate_memory_area with the hypervisor.
> Use pv_time_ops.steal_clock to account for stolen ticks.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> 
> Changes in v3:
> - use BUG_ON and smp_processor_id.
> ---
>  arch/arm/xen/enlighten.c |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 13609e0..dfa7738 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -14,7 +14,10 @@
>  #include <xen/xen-ops.h>
>  #include <asm/xen/hypervisor.h>
>  #include <asm/xen/hypercall.h>
> +#include <asm/arch_timer.h>
>  #include <asm/system_misc.h>
> +#include <asm/paravirt.h>
> +#include <linux/jump_label.h>
>  #include <linux/interrupt.h>
>  #include <linux/irqreturn.h>
>  #include <linux/module.h>
> @@ -152,6 +155,19 @@ int xen_unmap_domain_mfn_range(struct vm_area_struct *vma,
>  }
>  EXPORT_SYMBOL_GPL(xen_unmap_domain_mfn_range);
>  
> +unsigned long long xen_stolen_accounting(int cpu)
> +{
> +	struct vcpu_runstate_info state;
> +
> +	BUG_ON(cpu != smp_processor_id());
> +
> +	xen_get_runstate_snapshot(&state);
> +
> +	WARN_ON(state.state != RUNSTATE_running);
> +
> +	return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> +}
> +
>  static void __init xen_percpu_init(void *unused)
>  {
>  	struct vcpu_register_vcpu_info info;
> @@ -169,6 +185,8 @@ static void __init xen_percpu_init(void *unused)
>  	BUG_ON(err);
>  	per_cpu(xen_vcpu, cpu) = vcpup;
>  
> +	xen_setup_runstate_info(cpu);
> +
>  	enable_percpu_irq(xen_events_irq, 0);
>  }
>  
> @@ -300,6 +318,10 @@ static int __init xen_init_events(void)
>  
>  	on_each_cpu(xen_percpu_init, NULL, 0);
>  
> +	pv_time_ops.steal_clock = xen_stolen_accounting;

What guarantee do we have that this is done before the rest of the
kernel calls paravirt_steal_clock()? What if we have Xen support enabled
but don't run as a Xen guest?

> +	static_key_slow_inc(&paravirt_steal_enabled);
> +	static_key_slow_inc(&paravirt_steal_rq_enabled);
> +
>  	return 0;
>  }
>  postcore_initcall(xen_init_events);
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

Re: [PATCH v3 4/4] xen/arm: account for stolen ticks

[Stefano Stabellini]

On Wed, 8 May 2013, Marc Zyngier wrote:
> Hi Stefano,
> 
> On 08/05/13 16:41, Stefano Stabellini wrote:
> > Register the runstate_memory_area with the hypervisor.
> > Use pv_time_ops.steal_clock to account for stolen ticks.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > 
> > Changes in v3:
> > - use BUG_ON and smp_processor_id.
> > ---
> >  arch/arm/xen/enlighten.c |   22 ++++++++++++++++++++++
> >  1 files changed, 22 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > index 13609e0..dfa7738 100644
> > --- a/arch/arm/xen/enlighten.c
> > +++ b/arch/arm/xen/enlighten.c
> > @@ -14,7 +14,10 @@
> >  #include <xen/xen-ops.h>
> >  #include <asm/xen/hypervisor.h>
> >  #include <asm/xen/hypercall.h>
> > +#include <asm/arch_timer.h>
> >  #include <asm/system_misc.h>
> > +#include <asm/paravirt.h>
> > +#include <linux/jump_label.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/irqreturn.h>
> >  #include <linux/module.h>
> > @@ -152,6 +155,19 @@ int xen_unmap_domain_mfn_range(struct vm_area_struct *vma,
> >  }
> >  EXPORT_SYMBOL_GPL(xen_unmap_domain_mfn_range);
> >  
> > +unsigned long long xen_stolen_accounting(int cpu)
> > +{
> > +	struct vcpu_runstate_info state;
> > +
> > +	BUG_ON(cpu != smp_processor_id());
> > +
> > +	xen_get_runstate_snapshot(&state);
> > +
> > +	WARN_ON(state.state != RUNSTATE_running);
> > +
> > +	return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> > +}
> > +
> >  static void __init xen_percpu_init(void *unused)
> >  {
> >  	struct vcpu_register_vcpu_info info;
> > @@ -169,6 +185,8 @@ static void __init xen_percpu_init(void *unused)
> >  	BUG_ON(err);
> >  	per_cpu(xen_vcpu, cpu) = vcpup;
> >  
> > +	xen_setup_runstate_info(cpu);
> > +
> >  	enable_percpu_irq(xen_events_irq, 0);
> >  }
> >  
> > @@ -300,6 +318,10 @@ static int __init xen_init_events(void)
> >  
> >  	on_each_cpu(xen_percpu_init, NULL, 0);
> >  
> > +	pv_time_ops.steal_clock = xen_stolen_accounting;
> 
> What guarantee do we have that this is done before the rest of the
> kernel calls paravirt_steal_clock()?

That's not a problem: paravirt_steal_clock is not called unless
paravirt_steal_enabled or paravirt_steal_rq_enabled are set. Also
steal_clock is always increasing so loosing the first few updates is not
an issue.


> What if we have Xen support enabled but don't run as a Xen guest?

That's fine as long as the Xen runstate_memory_area interface is
available.
Usually I am a great fun of feature flags, so that every feature can be
dynamically enabled or disabled and an hypervisor interface can be only
partially implemented.

However the runstate_memory_area is very old and I would consider it
one of the core interfaces that need to be available in order to claim
"Xen compatibility".


> > +	static_key_slow_inc(&paravirt_steal_enabled);
> > +	static_key_slow_inc(&paravirt_steal_rq_enabled);
> > +
> >  	return 0;
> >  }
> >  postcore_initcall(xen_init_events);
> > 

Re: [Xen-devel] [PATCH v3 4/4] xen/arm: account for stolen ticks

[Ian Campbell]

On Wed, 2013-05-08 at 18:03 +0100, Stefano Stabellini wrote:
> > What if we have Xen support enabled but don't run as a Xen guest?
> 
> That's fine as long as the Xen runstate_memory_area interface is
> available.
> Usually I am a great fun of feature flags, so that every feature can be
> dynamically enabled or disabled and an hypervisor interface can be only
> partially implemented.
> 
> However the runstate_memory_area is very old and I would consider it
> one of the core interfaces that need to be available in order to claim
> "Xen compatibility".

I think Marc meant "what if CONFIG_XEN=y but we are running on KVM?". In
that case we wont have set either of the paravirt_steal*_enabled static
keys and so the hook won't be called.

> > > +	static_key_slow_inc(&paravirt_steal_enabled);
> > > +	static_key_slow_inc(&paravirt_steal_rq_enabled);
> > > +


Ian.