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Subject: x86: Support for lazy preemption
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu Nov 1 11:03:47 2012 +0100
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.3-rt21.tar.xz
From: Thomas Gleixner <tglx@linutronix.de>
Implement the x86 pieces for lazy preempt.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/preempt.h | 33 ++++++++++++++++++++++++++++++++-
arch/x86/include/asm/thread_info.h | 7 +++++++
include/linux/entry-common.h | 2 +-
kernel/entry/common.c | 2 +-
5 files changed, 42 insertions(+), 3 deletions(-)
---
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -231,6 +231,7 @@ config X86
select HAVE_PCI
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
+ select HAVE_PREEMPT_LAZY
select MMU_GATHER_RCU_TABLE_FREE if PARAVIRT
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_REGS_AND_STACK_ACCESS_API
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -90,17 +90,48 @@ static __always_inline void __preempt_co
* a decrement which hits zero means we have no preempt_count and should
* reschedule.
*/
-static __always_inline bool __preempt_count_dec_and_test(void)
+static __always_inline bool ____preempt_count_dec_and_test(void)
{
return GEN_UNARY_RMWcc("decl", __preempt_count, e, __percpu_arg([var]));
}
+static __always_inline bool __preempt_count_dec_and_test(void)
+{
+ if (____preempt_count_dec_and_test())
+ return true;
+#ifdef CONFIG_PREEMPT_LAZY
+ if (preempt_count())
+ return false;
+ if (current_thread_info()->preempt_lazy_count)
+ return false;
+ return test_thread_flag(TIF_NEED_RESCHED_LAZY);
+#else
+ return false;
+#endif
+}
+
/*
* Returns true when we need to resched and can (barring IRQ state).
*/
static __always_inline bool should_resched(int preempt_offset)
{
+#ifdef CONFIG_PREEMPT_LAZY
+ u32 tmp;
+ tmp = raw_cpu_read_4(__preempt_count);
+ if (tmp == preempt_offset)
+ return true;
+
+ /* preempt count == 0 ? */
+ tmp &= ~PREEMPT_NEED_RESCHED;
+ if (tmp != preempt_offset)
+ return false;
+ /* XXX PREEMPT_LOCK_OFFSET */
+ if (current_thread_info()->preempt_lazy_count)
+ return false;
+ return test_thread_flag(TIF_NEED_RESCHED_LAZY);
+#else
return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
+#endif
}
#ifdef CONFIG_PREEMPTION
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -57,11 +57,14 @@ struct thread_info {
unsigned long flags; /* low level flags */
unsigned long syscall_work; /* SYSCALL_WORK_ flags */
u32 status; /* thread synchronous flags */
+ int preempt_lazy_count; /* 0 => lazy preemptable
+ <0 => BUG */
};
#define INIT_THREAD_INFO(tsk) \
{ \
.flags = 0, \
+ .preempt_lazy_count = 0, \
}
#else /* !__ASSEMBLY__ */
@@ -90,6 +93,7 @@ struct thread_info {
#define TIF_NOTSC 16 /* TSC is not accessible in userland */
#define TIF_NOTIFY_SIGNAL 17 /* signal notifications exist */
#define TIF_SLD 18 /* Restore split lock detection on context switch */
+#define TIF_NEED_RESCHED_LAZY 19 /* lazy rescheduling necessary */
#define TIF_MEMDIE 20 /* is terminating due to OOM killer */
#define TIF_POLLING_NRFLAG 21 /* idle is polling for TIF_NEED_RESCHED */
#define TIF_IO_BITMAP 22 /* uses I/O bitmap */
@@ -114,6 +118,7 @@ struct thread_info {
#define _TIF_NOTSC (1 << TIF_NOTSC)
#define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL)
#define _TIF_SLD (1 << TIF_SLD)
+#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY)
#define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG)
#define _TIF_IO_BITMAP (1 << TIF_IO_BITMAP)
#define _TIF_SPEC_FORCE_UPDATE (1 << TIF_SPEC_FORCE_UPDATE)
@@ -145,6 +150,8 @@ struct thread_info {
#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)
+#define _TIF_NEED_RESCHED_MASK (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)
+
#define STACK_WARN (THREAD_SIZE/8)
/*
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -59,7 +59,7 @@
#define EXIT_TO_USER_MODE_WORK \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
- _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
+ _TIF_NEED_RESCHED_MASK | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
ARCH_EXIT_TO_USER_MODE_WORK)
/**
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -159,7 +159,7 @@ static unsigned long exit_to_user_mode_l
local_irq_enable_exit_to_user(ti_work);
- if (ti_work & _TIF_NEED_RESCHED)
+ if (ti_work & _TIF_NEED_RESCHED_MASK)
schedule();
#ifdef ARCH_RT_DELAYS_SIGNAL_SEND
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