[Xen-devel] [PATCH v10 3/5] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Acked-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
CC: linux@xxxxxxxxxxxxxxxx
CC: will.deacon@xxxxxxx
CC: nico@xxxxxxxxxx
CC: marc.zyngier@xxxxxxx
CC: cov@xxxxxxxxxxxxxx
CC: arnd@xxxxxxxx
CC: olof@xxxxxxxxx

---

Changes in v10:
- replace "---help---" with "help"

Changes in v7:
- ifdef CONFIG_PARAVIRT the content of paravirt.h.

Changes in v3:
- improve commit description and Kconfig help text;
- no need to initialize pv_time_ops;
- add PARAVIRT_TIME_ACCOUNTING.
---
 arch/arm/Kconfig                |   20 ++++++++++++++++++++
 arch/arm/include/asm/paravirt.h |   20 ++++++++++++++++++++
 arch/arm/kernel/Makefile        |    1 +
 arch/arm/kernel/paravirt.c      |   25 +++++++++++++++++++++++++
 4 files changed, 66 insertions(+)
 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 639411f..8dfdaa6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1819,6 +1819,25 @@ config SWIOTLB
 config IOMMU_HELPER
        def_bool SWIOTLB
 
+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_DOM0
        def_bool y
        depends on XEN
@@ -1832,6 +1851,7 @@ config XEN
        select ARCH_DMA_ADDR_T_64BIT
        select ARM_PSCI
        select SWIOTLB_XEN
+       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..8435ff59
--- /dev/null
+++ b/arch/arm/include/asm/paravirt.h
@@ -0,0 +1,20 @@
+#ifndef _ASM_ARM_PARAVIRT_H
+#define _ASM_ARM_PARAVIRT_H
+
+#ifdef CONFIG_PARAVIRT
+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
+
+#endif
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index af9e59b..3e6e937 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -81,6 +81,7 @@ obj-$(CONFIG_VDSO)            += vdso.o
 ifneq ($(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@xxxxxxxxxxxxx>
+ */
+
+#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);
-- 
1.7.10.4


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