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authorPeter Zijlstra <peterz@infradead.org>2013-08-14 12:51:00 (GMT)
committerIngo Molnar <mingo@kernel.org>2013-09-25 12:07:57 (GMT)
commitc2daa3bed53a81171cf8c1a36db798e82b91afe8 (patch)
treea7a7b1676e3101b986276f9ec0eab0ab5183e1ed /arch/x86/kernel/process_64.c
parenta233f1120c37724938f7201fe2353b2577adaaf9 (diff)
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@linux-foundation.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/n/tip-gzn5rfsf8trgjoqx8hyayy3q@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/process_64.c')
-rw-r--r--arch/x86/kernel/process_64.c8
1 files changed, 8 insertions, 0 deletions
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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