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timer: Allocate per-cpu tvec_base's statically

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Viresh 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2015-03-31 20:49:00 +05:30 committed by Ingo Molnar
parent 345527b1ed
commit b337a9380f
1 changed files with 19 additions and 29 deletions
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48
kernel/time/timer.c
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@ -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);