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.
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
arch/arm64/Kconfig | 10 ++++++++++
arch/arm64/include/asm/cpuidle_haltpoll.h | 9 +++++++++
arch/arm64/kernel/cpuidle.c | 23 +++++++++++++++++++++++
3 files changed, 42 insertions(+)
create mode 100644 arch/arm64/include/asm/cpuidle_haltpoll.h
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5d91259ee7b5..cf1c6681eb0a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -35,6 +35,7 @@ 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
@@ -2376,6 +2377,15 @@ 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..65f289407a6c
--- /dev/null
+++ b/arch/arm64/include/asm/cpuidle_haltpoll.h
@@ -0,0 +1,9 @@
+/* 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/cpuidle.c b/arch/arm64/kernel/cpuidle.c
index f372295207fb..334df82a0eac 100644
--- a/arch/arm64/kernel/cpuidle.c
+++ b/arch/arm64/kernel/cpuidle.c
@@ -72,3 +72,26 @@ __cpuidle int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
lpi->index, state);
}
#endif
+
+#if IS_ENABLED(CONFIG_HALTPOLL_CPUIDLE)
+
+#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_enable().
+ *
+ * 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);
+#endif
--
2.43.5
