On 2024/8/13 上午6:48, Ankur Arora wrote:
maobibo <maobibo@xxxxxxxxxxx> writes:
On 2024/7/27 上午4:21, Ankur Arora wrote:
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) { }
It is better that guest supports halt poll on more architectures, LoongArch
wants this if result is good.
Do we need disable halt polling on host hypervisor if guest also uses halt
polling idle method?
Yes. The intent is to work on that separately from this series. As the comment
below states, until that is available we only allow force loading.
Thanks for your explanation. By internal test, it is useful for
LoongArch virtmachine on some scenarios. And in late we want to add
haltpoll support on LoongArch VM based your series.
Regards
Bibo Mao
+
+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
--
ankur
