From da69dbf20c66f9416307996dd025edaa49931fb2 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 1 Nov 2012 11:03:47 +0100 Subject: [PATCH 260/323] x86: Support for lazy preemption Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.215-rt107.tar.xz Implement the x86 pieces for lazy preempt. Signed-off-by: Thomas Gleixner Signed-off-by: Luis Claudio R. Goncalves --- arch/x86/Kconfig | 1 + arch/x86/include/asm/preempt.h | 33 +++++++++++++++++++++++++++++- arch/x86/include/asm/thread_info.h | 11 ++++++++++ include/linux/entry-common.h | 6 +++--- kernel/entry/common.c | 2 +- 5 files changed, 48 insertions(+), 5 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 79e2b63eba407..f461b699c25d0 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -213,6 +213,7 @@ 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 diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index 50e0c0ab7b97b..afe37a8c6c248 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -89,17 +89,48 @@ static __always_inline void __preempt_count_sub(int val) * 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 diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 012c8ee93b67f..d77e99ba76102 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -56,17 +56,24 @@ struct task_struct; struct thread_info { unsigned long flags; /* low level 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__ */ #include +#define GET_THREAD_INFO(reg) \ + _ASM_MOV PER_CPU_VAR(cpu_current_top_of_stack),reg ; \ + _ASM_SUB $(THREAD_SIZE),reg ; + #endif /* @@ -103,6 +110,7 @@ struct thread_info { #define TIF_SYSCALL_TRACEPOINT 28 /* syscall tracepoint instrumentation */ #define TIF_ADDR32 29 /* 32-bit address space on 64 bits */ #define TIF_X32 30 /* 32-bit native x86-64 binary */ +#define TIF_NEED_RESCHED_LAZY 31 /* lazy rescheduling necessary */ #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) @@ -124,6 +132,7 @@ struct thread_info { #define _TIF_IA32 (1 << TIF_IA32) #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_FORCED_TF (1 << TIF_FORCED_TF) @@ -156,6 +165,8 @@ 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) /* diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index 46c42479f9501..b902af13d05fd 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -67,9 +67,9 @@ # define ARCH_EXIT_TO_USER_MODE_WORK (0) #endif -#define EXIT_TO_USER_MODE_WORK \ - (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ - _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \ +#define EXIT_TO_USER_MODE_WORK \ + (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ + _TIF_NEED_RESCHED_MASK | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \ ARCH_EXIT_TO_USER_MODE_WORK) /** diff --git a/kernel/entry/common.c b/kernel/entry/common.c index f32250adb6815..cdf97ea30b4c0 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -157,7 +157,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, 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 -- 2.44.0