From: Peter Zijlstra peterz@infradead.org
Memory for tvec_base is allocated separately for 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).
Cc: Thomas Gleixner tglx@linutronix.de Cc: linaro-kernel@lists.linaro.org Cc: Ingo Molnar mingo@redhat.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org --- kernel/time/timer.c | 48 +++++++++++++++++++----------------------------- 1 file 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);