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Date: Wed, 25 Sep 2013 09:39:32 -0700
From: tip-bot for Peter Zijlstra <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
torvalds@...ux-foundation.org, peterz@...radead.org,
tglx@...utronix.de
Subject: [tip:sched/core] sched, x86:
Provide a per-cpu preempt_count implementation
Commit-ID: c2daa3bed53a81171cf8c1a36db798e82b91afe8
Gitweb: http://git.kernel.org/tip/c2daa3bed53a81171cf8c1a36db798e82b91afe8
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 14 Aug 2013 14:51:00 +0200
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 25 Sep 2013 14:07:57 +0200
sched, x86: Provide a per-cpu preempt_count implementation
Convert x86 to use a per-cpu preemption count. The reason for doing so
is that accessing per-cpu variables is a lot cheaper than accessing
thread_info variables.
We still need to save/restore the actual preemption count due to
PREEMPT_ACTIVE so we place the per-cpu __preempt_count variable in the
same cache-line as the other hot __switch_to() variables such as
current_task.
NOTE: this save/restore is required even for !PREEMPT kernels as
cond_resched() also relies on preempt_count's PREEMPT_ACTIVE to ignore
task_struct::state.
Also rename thread_info::preempt_count to ensure nobody is
'accidentally' still poking at it.
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/n/tip-gzn5rfsf8trgjoqx8hyayy3q@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/x86/include/asm/Kbuild | 1 -
.../asm-generic => arch/x86/include/asm}/preempt.h | 39 ++++++++++------------
arch/x86/include/asm/thread_info.h | 5 ++-
arch/x86/kernel/asm-offsets.c | 1 -
arch/x86/kernel/cpu/common.c | 5 +++
arch/x86/kernel/entry_32.S | 7 ++--
arch/x86/kernel/entry_64.S | 4 +--
arch/x86/kernel/irq_32.c | 4 ---
arch/x86/kernel/process_32.c | 8 +++++
arch/x86/kernel/process_64.c | 8 +++++
10 files changed, 43 insertions(+), 39 deletions(-)
diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index eca2028..7f66985 100644
--- a/arch/x86/include/asm/Kbuild
+++ b/arch/x86/include/asm/Kbuild
@@ -5,4 +5,3 @@ genhdr-y += unistd_64.h
genhdr-y += unistd_x32.h
generic-y += clkdev.h
-generic-y += preempt.h
diff --git a/include/asm-generic/preempt.h b/arch/x86/include/asm/preempt.h
similarity index 65%
copy from include/asm-generic/preempt.h
copy to arch/x86/include/asm/preempt.h
index 82d958f..1309942 100644
--- a/include/asm-generic/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -1,44 +1,39 @@
#ifndef __ASM_PREEMPT_H
#define __ASM_PREEMPT_H
+#include <asm/rmwcc.h>
+#include <asm/percpu.h>
#include <linux/thread_info.h>
+DECLARE_PER_CPU(int, __preempt_count);
+
/*
* We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
* that think a non-zero value indicates we cannot preempt.
*/
static __always_inline int preempt_count(void)
{
- return current_thread_info()->preempt_count & ~PREEMPT_NEED_RESCHED;
-}
-
-static __always_inline int *preempt_count_ptr(void)
-{
- return ¤t_thread_info()->preempt_count;
+ return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
}
-/*
- * We now loose PREEMPT_NEED_RESCHED and cause an extra reschedule; however the
- * alternative is loosing a reschedule. Better schedule too often -- also this
- * should be a very rare operation.
- */
static __always_inline void preempt_count_set(int pc)
{
- *preempt_count_ptr() = pc;
+ __this_cpu_write_4(__preempt_count, pc);
}
/*
* must be macros to avoid header recursion hell
*/
#define task_preempt_count(p) \
- (task_thread_info(p)->preempt_count & ~PREEMPT_NEED_RESCHED)
+ (task_thread_info(p)->saved_preempt_count & ~PREEMPT_NEED_RESCHED)
#define init_task_preempt_count(p) do { \
- task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \
+ task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \
} while (0)
#define init_idle_preempt_count(p, cpu) do { \
- task_thread_info(p)->preempt_count = PREEMPT_ENABLED; \
+ task_thread_info(p)->saved_preempt_count = PREEMPT_ENABLED; \
+ per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \
} while (0)
/*
@@ -52,17 +47,17 @@ static __always_inline void preempt_count_set(int pc)
static __always_inline void set_preempt_need_resched(void)
{
- *preempt_count_ptr() &= ~PREEMPT_NEED_RESCHED;
+ __this_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
}
static __always_inline void clear_preempt_need_resched(void)
{
- *preempt_count_ptr() |= PREEMPT_NEED_RESCHED;
+ __this_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
}
static __always_inline bool test_preempt_need_resched(void)
{
- return !(*preempt_count_ptr() & PREEMPT_NEED_RESCHED);
+ return !(__this_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
}
/*
@@ -71,17 +66,17 @@ static __always_inline bool test_preempt_need_resched(void)
static __always_inline void __preempt_count_add(int val)
{
- *preempt_count_ptr() += val;
+ __this_cpu_add_4(__preempt_count, val);
}
static __always_inline void __preempt_count_sub(int val)
{
- *preempt_count_ptr() -= val;
+ __this_cpu_add_4(__preempt_count, -val);
}
static __always_inline bool __preempt_count_dec_and_test(void)
{
- return !--*preempt_count_ptr();
+ GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), "e");
}
/*
@@ -97,7 +92,7 @@ static __always_inline bool need_resched(void)
*/
static __always_inline bool should_resched(void)
{
- return unlikely(!*preempt_count_ptr());
+ return unlikely(!__this_cpu_read_4(__preempt_count));
}
#endif /* __ASM_PREEMPT_H */
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 2781119..c46a46b 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -28,8 +28,7 @@ struct thread_info {
__u32 flags; /* low level flags */
__u32 status; /* thread synchronous flags */
__u32 cpu; /* current CPU */
- int preempt_count; /* 0 => preemptable,
- <0 => BUG */
+ int saved_preempt_count;
mm_segment_t addr_limit;
struct restart_block restart_block;
void __user *sysenter_return;
@@ -49,7 +48,7 @@ struct thread_info {
.exec_domain = &default_exec_domain, \
.flags = 0, \
.cpu = 0, \
- .preempt_count = INIT_PREEMPT_COUNT, \
+ .saved_preempt_count = INIT_PREEMPT_COUNT, \
.addr_limit = KERNEL_DS, \
.restart_block = { \
.fn = do_no_restart_syscall, \
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 2861082..9f6b934 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -32,7 +32,6 @@ void common(void) {
OFFSET(TI_flags, thread_info, flags);
OFFSET(TI_status, thread_info, status);
OFFSET(TI_addr_limit, thread_info, addr_limit);
- OFFSET(TI_preempt_count, thread_info, preempt_count);
BLANK();
OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 2793d1f..5223fe6 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1095,6 +1095,9 @@ DEFINE_PER_CPU(char *, irq_stack_ptr) =
DEFINE_PER_CPU(unsigned int, irq_count) __visible = -1;
+DEFINE_PER_CPU(int, __preempt_count) = INIT_PREEMPT_COUNT;
+EXPORT_PER_CPU_SYMBOL(__preempt_count);
+
DEFINE_PER_CPU(struct task_struct *, fpu_owner_task);
/*
@@ -1169,6 +1172,8 @@ void debug_stack_reset(void)
DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
EXPORT_PER_CPU_SYMBOL(current_task);
+DEFINE_PER_CPU(int, __preempt_count) = INIT_PREEMPT_COUNT;
+EXPORT_PER_CPU_SYMBOL(__preempt_count);
DEFINE_PER_CPU(struct task_struct *, fpu_owner_task);
#ifdef CONFIG_CC_STACKPROTECTOR
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index f0dcb0c..fd1bc1b 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -362,12 +362,9 @@ END(ret_from_exception)
#ifdef CONFIG_PREEMPT
ENTRY(resume_kernel)
DISABLE_INTERRUPTS(CLBR_ANY)
- cmpl $0,TI_preempt_count(%ebp) # non-zero preempt_count ?
- jnz restore_all
need_resched:
- movl TI_flags(%ebp), %ecx # need_resched set ?
- testb $_TIF_NEED_RESCHED, %cl
- jz restore_all
+ cmpl $0,PER_CPU_VAR(__preempt_count)
+ jnz restore_all
testl $X86_EFLAGS_IF,PT_EFLAGS(%esp) # interrupts off (exception path) ?
jz restore_all
call preempt_schedule_irq
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1b69951..6a43e7d 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1118,10 +1118,8 @@ retint_signal:
/* Returning to kernel space. Check if we need preemption */
/* rcx: threadinfo. interrupts off. */
ENTRY(retint_kernel)
- cmpl $0,TI_preempt_count(%rcx)
+ cmpl $0,PER_CPU_VAR(__preempt_count)
jnz retint_restore_args
- bt $TIF_NEED_RESCHED,TI_flags(%rcx)
- jnc retint_restore_args
bt $9,EFLAGS-ARGOFFSET(%rsp) /* interrupts off? */
jnc retint_restore_args
call preempt_schedule_irq
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 4186755..3fe0663 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -100,9 +100,6 @@ execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
irqctx->tinfo.task = curctx->tinfo.task;
irqctx->tinfo.previous_esp = current_stack_pointer;
- /* Copy the preempt_count so that the [soft]irq checks work. */
- irqctx->tinfo.preempt_count = curctx->tinfo.preempt_count;
-
if (unlikely(overflow))
call_on_stack(print_stack_overflow, isp);
@@ -131,7 +128,6 @@ void irq_ctx_init(int cpu)
THREAD_SIZE_ORDER));
memset(&irqctx->tinfo, 0, sizeof(struct thread_info));
irqctx->tinfo.cpu = cpu;
- irqctx->tinfo.preempt_count = HARDIRQ_OFFSET;
irqctx->tinfo.addr_limit = MAKE_MM_SEG(0);
per_cpu(hardirq_ctx, cpu) = irqctx;
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 884f98f..c2ec1aa 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -292,6 +292,14 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
set_iopl_mask(next->iopl);
/*
+ * If it were not for PREEMPT_ACTIVE we could guarantee that the
+ * preempt_count of all tasks was equal here and this would not be
+ * needed.
+ */
+ task_thread_info(prev_p)->saved_preempt_count = this_cpu_read(__preempt_count);
+ this_cpu_write(__preempt_count, task_thread_info(next_p)->saved_preempt_count);
+
+ /*
* Now maybe handle debug registers and/or IO bitmaps
*/
if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index bb1dc51..45ab4d6 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -363,6 +363,14 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
this_cpu_write(old_rsp, next->usersp);
this_cpu_write(current_task, next_p);
+ /*
+ * If it were not for PREEMPT_ACTIVE we could guarantee that the
+ * preempt_count of all tasks was equal here and this would not be
+ * needed.
+ */
+ task_thread_info(prev_p)->saved_preempt_count = this_cpu_read(__preempt_count);
+ this_cpu_write(__preempt_count, task_thread_info(next_p)->saved_preempt_count);
+
this_cpu_write(kernel_stack,
(unsigned long)task_stack_page(next_p) +
THREAD_SIZE - KERNEL_STACK_OFFSET);
--
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