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@xxxxxxxxxx>
Tested-by: Misono Tomohiro <misono.tomohiro@xxxxxxxxxxx>
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
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
