abf917cd91
If we want to stop the tick further idle, we need to be able to account the cputime without using the tick. Virtual based cputime accounting solves that problem by hooking into kernel/user boundaries. However implementing CONFIG_VIRT_CPU_ACCOUNTING require low level hooks and involves more overhead. But we already have a generic context tracking subsystem that is required for RCU needs by archs which plan to shut down the tick outside idle. This patch implements a generic virtual based cputime accounting that relies on these generic kernel/user hooks. There are some upsides of doing this: - This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING if context tracking is already built (already necessary for RCU in full tickless mode). - We can rely on the generic context tracking subsystem to dynamically (de)activate the hooks, so that we can switch anytime between virtual and tick based accounting. This way we don't have the overhead of the virtual accounting when the tick is running periodically. And one downside: - There is probably more overhead than a native virtual based cputime accounting. But this relies on hooks that are already set anyway. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
72 lines
1.8 KiB
C
72 lines
1.8 KiB
C
#include <linux/context_tracking.h>
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#include <linux/rcupdate.h>
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#include <linux/sched.h>
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#include <linux/hardirq.h>
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DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
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#ifdef CONFIG_CONTEXT_TRACKING_FORCE
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.active = true,
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#endif
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};
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void user_enter(void)
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{
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unsigned long flags;
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/*
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* Some contexts may involve an exception occuring in an irq,
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* leading to that nesting:
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* rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
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* This would mess up the dyntick_nesting count though. And rcu_irq_*()
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* helpers are enough to protect RCU uses inside the exception. So
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* just return immediately if we detect we are in an IRQ.
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*/
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if (in_interrupt())
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return;
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WARN_ON_ONCE(!current->mm);
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local_irq_save(flags);
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if (__this_cpu_read(context_tracking.active) &&
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__this_cpu_read(context_tracking.state) != IN_USER) {
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vtime_user_enter(current);
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rcu_user_enter();
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__this_cpu_write(context_tracking.state, IN_USER);
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}
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local_irq_restore(flags);
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}
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void user_exit(void)
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{
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unsigned long flags;
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/*
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* Some contexts may involve an exception occuring in an irq,
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* leading to that nesting:
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* rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
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* This would mess up the dyntick_nesting count though. And rcu_irq_*()
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* helpers are enough to protect RCU uses inside the exception. So
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* just return immediately if we detect we are in an IRQ.
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*/
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if (in_interrupt())
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return;
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local_irq_save(flags);
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if (__this_cpu_read(context_tracking.state) == IN_USER) {
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rcu_user_exit();
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vtime_user_exit(current);
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__this_cpu_write(context_tracking.state, IN_KERNEL);
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}
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local_irq_restore(flags);
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}
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void context_tracking_task_switch(struct task_struct *prev,
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struct task_struct *next)
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{
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if (__this_cpu_read(context_tracking.active)) {
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clear_tsk_thread_flag(prev, TIF_NOHZ);
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set_tsk_thread_flag(next, TIF_NOHZ);
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}
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}
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