Commit b337a938 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

timer: Allocate per-cpu tvec_base's statically 



Memory for the 'tvec_base' array is allocated separately for the boot CPU (statically)
and non-boot CPUs (dynamically).

The reason is because __TIMER_INITIALIZER() needs to set ->base to a
valid pointer (because we've made NULL special, hint: lock_timer_base())
and we cannot get a compile time pointer to per-cpu entries because we
don't know where we'll map the section, even for the boot cpu.

This can be simplified a bit by statically allocating per-cpu memory.
The only disadvantage is that memory for one of the structures will stay
unused, i.e. for the boot CPU, which uses boot_tvec_bases.

This will also guarantee that tvec_base is cacheline aligned. Even
though tvec_base has ____cacheline_aligned stuck on, kzalloc_node() does
not actually respect that (but guarantees a minimum u64 alignment).

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/17cdf560f2727f687ab159707d0aa591f8a2f82d.1427814611.git.viresh.kumar@linaro.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 345527b1

kernel/time/timer.c

+19 −29
Original line number Diff line number Diff line
@@ -90,8 +90,19 @@ struct tvec_base { 
	struct tvec tv5;

} ____cacheline_aligned;



/*

 * __TIMER_INITIALIZER() needs to set ->base to a valid pointer (because we've

 * made NULL special, hint: lock_timer_base()) and we cannot get a compile time

 * pointer to per-cpu entries because we don't know where we'll map the section,

 * even for the boot cpu.

 *

 * And so we use boot_tvec_bases for boot CPU and per-cpu __tvec_bases for the

 * rest of them.

 */

struct tvec_base boot_tvec_bases;

EXPORT_SYMBOL(boot_tvec_bases);

static DEFINE_PER_CPU(struct tvec_base, __tvec_bases);



static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases;



/* Functions below help us manage 'deferrable' flag */
@@ -1534,46 +1545,25 @@ EXPORT_SYMBOL(schedule_timeout_uninterruptible); 


static int init_timers_cpu(int cpu)

{

	int j;

	struct tvec_base *base;

	struct tvec_base *base = per_cpu(tvec_bases, cpu);

	static char tvec_base_done[NR_CPUS];

	int j;



	if (!tvec_base_done[cpu]) {

		static char boot_done;

		static char boot_cpu_skipped;



		if (boot_done) {

			/*

			 * The APs use this path later in boot

			 */

			base = kzalloc_node(sizeof(*base), GFP_KERNEL,

					    cpu_to_node(cpu));

			if (!base)

				return -ENOMEM;



			/* Make sure tvec_base has TIMER_FLAG_MASK bits free */

			if (WARN_ON(base != tbase_get_base(base))) {

				kfree(base);

				return -ENOMEM;

			}

			per_cpu(tvec_bases, cpu) = base;

		if (!boot_cpu_skipped) {

			boot_cpu_skipped = 1; /* skip the boot cpu */

		} else {

			/*

			 * This is for the boot CPU - we use compile-time

			 * static initialisation because per-cpu memory isn't

			 * ready yet and because the memory allocators are not

			 * initialised either.

			 */

			boot_done = 1;

			base = &boot_tvec_bases;

			base = per_cpu_ptr(&__tvec_bases, cpu);

			per_cpu(tvec_bases, cpu) = base;

		}



		spin_lock_init(&base->lock);

		tvec_base_done[cpu] = 1;

		base->cpu = cpu;

	} else {

		base = per_cpu(tvec_bases, cpu);

	}





	for (j = 0; j < TVN_SIZE; j++) {

		INIT_LIST_HEAD(base->tv5.vec + j);

		INIT_LIST_HEAD(base->tv4.vec + j);

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