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rcu: Simplify rcu_init_nohz() cpumask handling 

In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
Except that kernels booted without the rcu_nocbs= will not have
allocated rcu_nocb_mask.  And the current rcu_init_nohz() function uses
its need_rcu_nocb_mask and offload_all local variables to track the
rcu_nocb and nohz_full state.

But there is a much simpler approach, namely creating a cpumask pointer
to track the default and then using cpumask_available() to check the
rcu_nocb_mask state.  This commit takes this approach, thereby simplifying
and shortening the rcu_init_nohz() function.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Zhen Lei 2022-09-13 11:00:36 +08:00 committed by Paul E. McKenney
parent 9abf2313ad
commit f1ffec1ea3
1 changed files with 11 additions and 23 deletions
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34
kernel/rcu/tree_nocb.h
View File

@ -1210,45 +1210,33 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
void __init rcu_init_nohz(void)
{
int cpu;
bool need_rcu_nocb_mask = false;
bool offload_all = false;
struct rcu_data *rdp;
#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
if (!rcu_state.nocb_is_setup) {
need_rcu_nocb_mask = true;
offload_all = true;
}
#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
const struct cpumask *cpumask = NULL;
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
need_rcu_nocb_mask = true;
offload_all = false; /* NO_HZ_FULL has its own mask. */
}
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
cpumask = tick_nohz_full_mask;
#endif
if (need_rcu_nocb_mask) {
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&
!rcu_state.nocb_is_setup && !cpumask)
cpumask = cpu_possible_mask;
if (cpumask) {
if (!cpumask_available(rcu_nocb_mask)) {
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
return;
}
}
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
rcu_state.nocb_is_setup = true;
}
if (!rcu_state.nocb_is_setup)
return;
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running)
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
if (offload_all)
cpumask_setall(rcu_nocb_mask);
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
cpumask_and(rcu_nocb_mask, cpu_possible_mask,