This patchset enables the usage of haltpoll governer on arm64. This is
specifically interesting for KVM guests by reducing the IPC latencies.
Here are some benchmarks without/with haltpoll for a KVM guest:
a) without haltpoll:
perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes
Total time: 8.138 [sec]
8.138094 usecs/op
122878 ops/sec
b) with haltpoll:
perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes
Total time: 5.003 [sec]
5.003085 usecs/op
199876 ops/sec
v3 changes from v2:
- fix 1/7 per Petr Mladek - remove ARCH_HAS_CPU_RELAX from arch/x86/Kconfig
- add Ack-by from Rafael Wysocki on 2/7
v2 changes from v1:
- added patch 7 where we change cpu_relax with smp_cond_load_relaxed per PeterZ
(this improves by 50% at least the CPU cycles consumed in the tests above:
10,716,881,137 now vs 14,503,014,257 before)
- removed the ifdef from patch 1 per RafaelW
Joao Martins (6):
x86: Move ARCH_HAS_CPU_RELAX to arch
x86/kvm: Move haltpoll_want() to be arch defined
governors/haltpoll: Drop kvm_para_available() check
arm64: Select ARCH_HAS_CPU_RELAX
arm64: Define TIF_POLLING_NRFLAG
cpuidle-haltpoll: ARM64 support
Mihai Carabas (1):
cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
arch/Kconfig | 3 +++
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/thread_info.h | 6 ++++++
arch/x86/Kconfig | 4 +---
arch/x86/include/asm/cpuidle_haltpoll.h | 1 +
arch/x86/kernel/kvm.c | 10 ++++++++++
drivers/cpuidle/Kconfig | 4 ++--
drivers/cpuidle/cpuidle-haltpoll.c | 8 ++------
drivers/cpuidle/governors/haltpoll.c | 5 +----
drivers/cpuidle/poll_state.c | 14 +++++++++-----
include/linux/cpuidle_haltpoll.h | 5 +++++
11 files changed, 41 insertions(+), 20 deletions(-)
--
1.8.3.1
From: Joao Martins <[email protected]>
The default idle method for arm64 is WFI and it therefore
unconditionally requires the reschedule interrupt when idle.
Commit 842514849a61 ("arm64: Remove TIF_POLLING_NRFLAG") had
reverted it because WFI was the only idle method. ARM64 support
for haltpoll means that poll_idle() polls for TIF_POLLING_NRFLAG,
so define on arm64 *only if* haltpoll is built, using the same bit.
Signed-off-by: Joao Martins <[email protected]>
Signed-off-by: Mihai Carabas <[email protected]>
---
arch/arm64/include/asm/thread_info.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 553d1bc559c6..d3010d0b2988 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -69,6 +69,9 @@ struct thread_info {
#define TIF_SYSCALL_TRACEPOINT 10 /* syscall tracepoint for ftrace */
#define TIF_SECCOMP 11 /* syscall secure computing */
#define TIF_SYSCALL_EMU 12 /* syscall emulation active */
+#if IS_ENABLED(CONFIG_HALTPOLL_CPUIDLE) || IS_ENABLED(CONFIG_HALTPOLL_CPUIDLE_MODULE)
+#define TIF_POLLING_NRFLAG 16 /* poll_idle() polls TIF_NEED_RESCHED */
+#endif
#define TIF_MEMDIE 18 /* is terminating due to OOM killer */
#define TIF_FREEZE 19
#define TIF_RESTORE_SIGMASK 20
@@ -90,6 +93,9 @@ struct thread_info {
#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
+#if IS_ENABLED(CONFIG_HALTPOLL_CPUIDLE) || IS_ENABLED(CONFIG_HALTPOLL_CPUIDLE_MODULE)
+#define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG)
+#endif
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP)
#define _TIF_32BIT (1 << TIF_32BIT)
--
1.8.3.1
From: Joao Martins <[email protected]>
To test whether it's a guest or not for the default cases, the haltpoll
driver uses the kvm_para* helpers to find out if it's a guest or not.
ARM64 doesn't have or defined any of these, so it remains disabled on
the default. Although it allows to be force-loaded.
Signed-off-by: Joao Martins <[email protected]>
Signed-off-by: Mihai Carabas <[email protected]>
---
drivers/cpuidle/Kconfig | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index cac5997dca50..067927eda466 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -35,7 +35,7 @@ config CPU_IDLE_GOV_TEO
config CPU_IDLE_GOV_HALTPOLL
bool "Haltpoll governor (for virtualized systems)"
- depends on KVM_GUEST
+ depends on (X86 && KVM_GUEST) || ARM64
help
This governor implements haltpoll idle state selection, to be
used in conjunction with the haltpoll cpuidle driver, allowing
@@ -73,7 +73,7 @@ endmenu
config HALTPOLL_CPUIDLE
tristate "Halt poll cpuidle driver"
- depends on X86 && KVM_GUEST
+ depends on (X86 && KVM_GUEST) || ARM64
select CPU_IDLE_GOV_HALTPOLL
default y
help
--
1.8.3.1