nohz: Only enable context tracking on full dynticks CPUs (2e709338) · Commits · 戴 / test

The context tracking subsystem has the ability to selectively enable the tracking on any defined subset of CPU. This means that we can define a CPU range that doesn't run the context tracking and another range that does. Now what we want in practice is to enable the tracking on full dynticks CPUs only. In order to perform this, we just need to pass our full dynticks CPU range selection from the full dynticks subsystem to the context tracking. This way we can spare the overhead of RCU user extended quiescent state and vtime maintainance on the CPUs that are outside the full dynticks range. Just keep in mind the raw context tracking itself is still necessary everywhere. Signed-off-by:

Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Kevin Hilman <khilman@linaro.org>

include/linux/context_tracking.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -34,6 +34,8 @@ static inline bool context_tracking_active(void)
		return __this_cpu_read(context_tracking.active);
		}

		extern void context_tracking_cpu_set(int cpu);

		extern void user_enter(void);
		extern void user_exit(void);

kernel/context_tracking.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -26,6 +26,11 @@ DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
		#endif
		};

		void context_tracking_cpu_set(int cpu)
		{
		per_cpu(context_tracking.active, cpu) = true;
		}

		/**
		* user_enter - Inform the context tracking that the CPU is going to
		* enter userspace mode.

kernel/time/tick-sched.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -23,6 +23,7 @@
		#include <linux/irq_work.h>
		#include <linux/posix-timers.h>
		#include <linux/perf_event.h>
		#include <linux/context_tracking.h>

		#include <asm/irq_regs.h>

		@@ -344,11 +345,16 @@ static int tick_nohz_init_all(void)

		void __init tick_nohz_init(void)
		{
		int cpu;

		if (!have_nohz_full_mask) {
		if (tick_nohz_init_all() < 0)
		return;
		}

		for_each_cpu(cpu, nohz_full_mask)
		context_tracking_cpu_set(cpu);

		cpu_notifier(tick_nohz_cpu_down_callback, 0);
		cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
		pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);

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