Once the lazy preemption is supported, it would be desirable to change
the preemption models at runtime. So add support for dynamic preemption
using DYNAMIC_KEY.
::Tested lightly on Power10 LPAR
Performance numbers indicate that, preempt=none(no dynamic) and
preempt=none(dynamic) are close.
cat /sys/kernel/debug/sched/preempt
(none) voluntary full lazy
perf stat -e probe:__cond_resched -a sleep 1
Performance counter stats for 'system wide':
1,253 probe:__cond_resched
echo full > /sys/kernel/debug/sched/preempt
cat /sys/kernel/debug/sched/preempt
none voluntary (full) lazy
perf stat -e probe:__cond_resched -a sleep 1
Performance counter stats for 'system wide':
0 probe:__cond_resched
Signed-off-by: Shrikanth Hegde <sshe...@linux.ibm.com>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/preempt.h | 16 ++++++++++++++++
arch/powerpc/kernel/interrupt.c | 6 +++++-
arch/powerpc/lib/vmx-helper.c | 2 +-
4 files changed, 23 insertions(+), 2 deletions(-)
create mode 100644 arch/powerpc/include/asm/preempt.h
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 424f188e62d9..364edaea1f88 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -275,6 +275,7 @@ config PPC
select HAVE_PERF_EVENTS_NMI if PPC64
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
+ select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_RETHOOK if KPROBES
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE
diff --git a/arch/powerpc/include/asm/preempt.h
b/arch/powerpc/include/asm/preempt.h
new file mode 100644
index 000000000000..000e2b9681f3
--- /dev/null
+++ b/arch/powerpc/include/asm/preempt.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_POWERPC_PREEMPT_H
+#define __ASM_POWERPC_PREEMPT_H
+
+#include <asm-generic/preempt.h>
+
+#if defined(CONFIG_PREEMPT_DYNAMIC)
+#include <linux/jump_label.h>
+DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+#define need_irq_preemption() \
+ (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
+#else
+#define need_irq_preemption() (IS_ENABLED(CONFIG_PREEMPTION))
+#endif
+
+#endif /* __ASM_POWERPC_PREEMPT_H */
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 8f4acc55407b..e0c681d0b076 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -25,6 +25,10 @@
unsigned long global_dbcr0[NR_CPUS];
#endif
+#if defined(CONFIG_PREEMPT_DYNAMIC)
+DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+#endif
+
#ifdef CONFIG_PPC_BOOK3S_64
DEFINE_STATIC_KEY_FALSE(interrupt_exit_not_reentrant);
static inline bool exit_must_hard_disable(void)
@@ -396,7 +400,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct
pt_regs *regs)
/* Returning to a kernel context with local irqs enabled. */
WARN_ON_ONCE(!(regs->msr & MSR_EE));
again:
- if (IS_ENABLED(CONFIG_PREEMPTION)) {
+ if (need_irq_preemption()) {
/* Return to preemptible kernel context */
if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
if (preempt_count() == 0)
diff --git a/arch/powerpc/lib/vmx-helper.c b/arch/powerpc/lib/vmx-helper.c
index 58ed6bd613a6..54340912398f 100644
--- a/arch/powerpc/lib/vmx-helper.c
+++ b/arch/powerpc/lib/vmx-helper.c
@@ -45,7 +45,7 @@ int exit_vmx_usercopy(void)
* set and we are preemptible. The hack here is to schedule a
* decrementer to fire here and reschedule for us if necessary.
*/
- if (IS_ENABLED(CONFIG_PREEMPTION) && need_resched())
+ if (need_irq_preemption() && need_resched())
set_dec(1);
return 0;
}
--
2.39.3
