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: 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>

1 files changed, 19 insertions, 29 deletions

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 2d3f5c504939..f3cc653f876c 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -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);