[PATCH v7 09/10] arm64: support cpuidle-haltpoll

[Ankur Arora <ankur.a.arora@oracle.com>]

Add architectural support for cpuidle-haltpoll driver by defining
arch_haltpoll_*().

Also define ARCH_CPUIDLE_HALTPOLL to allow cpuidle-haltpoll to be
selected, and given that we have an optimized polling mechanism
in smp_cond_load*(), select ARCH_HAS_OPTIMIZED_POLL.

smp_cond_load*() are implemented via LDXR, WFE, with LDXR loading
a memory region in exclusive state and the WFE waiting for any
stores to it.

In the edge case -- no CPU stores to the waited region and there's no
interrupt -- the event-stream will provide the terminating condition
ensuring we don't wait forever, but because the event-stream runs at
a fixed frequency (configured at 10kHz) we might spend more time in
the polling stage than specified by cpuidle_poll_time().

This would only happen in the last iteration, since overshooting the
poll_limit means the governor moves out of the polling stage.

Tested-by: Haris Okanovic <harisokn@amazon.com>
Tested-by: Misono Tomohiro <misono.tomohiro@fujitsu.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/arm64/Kconfig                        | 10 ++++++++++
 arch/arm64/include/asm/cpuidle_haltpoll.h | 10 ++++++++++
 arch/arm64/kernel/Makefile                |  1 +
 arch/arm64/kernel/cpuidle_haltpoll.c      | 22 ++++++++++++++++++++++
 4 files changed, 43 insertions(+)
 create mode 100644 arch/arm64/include/asm/cpuidle_haltpoll.h
 create mode 100644 arch/arm64/kernel/cpuidle_haltpoll.c

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a2f8ff354ca6..9bd93ce2f9d9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -36,6 +36,7 @@ config ARM64
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+	select ARCH_HAS_OPTIMIZED_POLL
 	select ARCH_HAS_PTE_DEVMAP
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_HW_PTE_YOUNG
@@ -2385,6 +2386,15 @@ config ARCH_HIBERNATION_HEADER
 config ARCH_SUSPEND_POSSIBLE
 	def_bool y
 
+config ARCH_CPUIDLE_HALTPOLL
+	bool "Enable selection of the cpuidle-haltpoll driver"
+	default n
+	help
+	  cpuidle-haltpoll allows for adaptive polling based on
+	  current load before entering the idle state.
+
+	  Some virtualized workloads benefit from using it.
+
 endmenu # "Power management options"
 
 menu "CPU Power Management"
diff --git a/arch/arm64/include/asm/cpuidle_haltpoll.h b/arch/arm64/include/asm/cpuidle_haltpoll.h
new file mode 100644
index 000000000000..ed615a99803b
--- /dev/null
+++ b/arch/arm64/include/asm/cpuidle_haltpoll.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ARCH_HALTPOLL_H
+#define _ARCH_HALTPOLL_H
+
+static inline void arch_haltpoll_enable(unsigned int cpu) { }
+static inline void arch_haltpoll_disable(unsigned int cpu) { }
+
+bool arch_haltpoll_want(bool force);
+#endif
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 2b112f3b7510..bbfb57eda2f1 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -70,6 +70,7 @@ obj-$(CONFIG_ARM64_PTR_AUTH)		+= pointer_auth.o
 obj-$(CONFIG_ARM64_MTE)			+= mte.o
 obj-y					+= vdso-wrap.o
 obj-$(CONFIG_COMPAT_VDSO)		+= vdso32-wrap.o
+obj-$(CONFIG_ARCH_CPUIDLE_HALTPOLL)	+= cpuidle_haltpoll.o
 
 # Force dependency (vdso*-wrap.S includes vdso.so through incbin)
 $(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so
diff --git a/arch/arm64/kernel/cpuidle_haltpoll.c b/arch/arm64/kernel/cpuidle_haltpoll.c
new file mode 100644
index 000000000000..63fc5ebca79b
--- /dev/null
+++ b/arch/arm64/kernel/cpuidle_haltpoll.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+#include <clocksource/arm_arch_timer.h>
+#include <asm/cpuidle_haltpoll.h>
+
+bool arch_haltpoll_want(bool force)
+{
+	/*
+	 * Enabling haltpoll requires two things:
+	 *
+	 * - Event stream support to provide a terminating condition to the
+	 *   WFE in the poll loop.
+	 *
+	 * - KVM support for arch_haltpoll_enable(), arch_haltpoll_disable().
+	 *
+	 * Given that the second is missing, allow haltpoll to only be force
+	 * loaded.
+	 */
+	return (arch_timer_evtstrm_available() && false) || force;
+}
+EXPORT_SYMBOL_GPL(arch_haltpoll_want);
-- 
2.43.5