* Viresh Kumar viresh.kumar@linaro.org wrote:
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).
Signed-off-by: Peter Zijlstra peterz@infradead.org Signed-off-by: Viresh Kumar viresh.kumar@linaro.org
kernel/time/timer.c | 36 ++++++++---------------------------- 1 file changed, 8 insertions(+), 28 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 2d3f5c504939..6e8220ec8a62 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -93,6 +93,7 @@ struct tvec_base { struct tvec_base boot_tvec_bases; EXPORT_SYMBOL(boot_tvec_bases); static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases; +static DEFINE_PER_CPU(struct tvec_base, __tvec_bases); /* Functions below help us manage 'deferrable' flag */ static inline unsigned int tbase_get_deferrable(struct tvec_base *base) @@ -1534,46 +1535,25 @@ 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;
if (!boot_done) {boot_done = 1; /* skip the boot cpu */
So it would be a lot more descriptive to name this flag 'boot_cpu_skipped'?
} else {
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; }
Also, I'd put a description about the PER_CPU background into comments as well, because it's not obvious at first sight at all what the whole (boot_tvec_bases, tvec_bases, __tvec_bases) dance does.
Thanks,
Ingo