On 11/4/22 16:00, Tejun Heo wrote:
On Fri, Nov 04, 2022 at 02:20:50PM -0400, Waiman Long wrote:+/** + * cgroup_rstat_css_flush - flush stats for the given css and cpu + * @css: target css to be flush + * @cpu: the cpu that holds the stats to be flush + * + * A lightweight rstat flush operation for a given css and cpu. + * Only the cpu_lock is being held for mutual exclusion, the cgroup_rstat_lock + * isn't used. + */ +void cgroup_rstat_css_flush(struct cgroup_subsys_state *css, int cpu) +{ + raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu); + + raw_spin_lock_irq(cpu_lock); + rcu_read_lock(); + css->ss->css_rstat_flush(css, cpu); + rcu_read_unlock(); + raw_spin_unlock_irq(cpu_lock); +}Would it make sense to itereate CPUs within the helper rather than asking the caller to do it? Also, in terms of patch sequencing, this introduces a bug and then fixes it. Prolly better to not introduce the bug in the first place. Thanks.
I should have named the function cgroup_rstat_css_cpu_flush() to indicate that the cpu is a needed parameter. We can have a cgroup_rstat_css_flush() in the future if the need arises.
It is an optimization to call this function only if the corresponding cpu has a pending lockless list. I could do cpu iteration here and call the flushing function for all the CPUs. It is less optimized this way. Since it is a slow path, I guess performance is not that critical. So I can go either way. Please let me know your preference.
Thanks, Longman
