Re: [PATCH v7 1/4] lib/percpu-list: Per-cpu list with associated per-cpu locks

[Waiman Long]

On 04/14/2016 10:10 AM, Jan Kara wrote:
> On Tue 12-04-16 18:54:43, Waiman Long wrote:
> > Linked list is used everywhere in the Linux kernel. However, if many
> > threads are trying to add or delete entries into the same linked list,
> > it can create a performance bottleneck.
> >
> > This patch introduces a new per-cpu list subystem with associated
> > per-cpu locks for protecting each of the lists individually. This
> > allows list entries insertion and deletion operations to happen in
> > parallel instead of being serialized with a global list and lock.
> >
> > List entry insertion is strictly per cpu. List deletion, however, can
> > happen in a cpu other than the one that did the insertion. So we still
> > need lock to protect the list. Because of that, there may still be
> > a small amount of contention when deletion is being done.
> >
> > A new header file include/linux/percpu-list.h will be added with the
> > associated pcpu_list_head and pcpu_list_node structures. The following
> > functions are provided to manage the per-cpu list:
> >
> >   1. int init_pcpu_list_head(struct pcpu_list_head **ppcpu_head)
> >   2. void pcpu_list_add(struct pcpu_list_node *node,
> > 		       struct pcpu_list_head *head)
> >   3. void pcpu_list_del(struct pcpu_list *node)
> >
> > Iteration of all the list entries within a group of per-cpu
> > lists is done by calling either the pcpu_list_iterate() or
> > pcpu_list_iterate_safe() functions in a while loop. They correspond
> > to the list_for_each_entry() and list_for_each_entry_safe() macros
> > respectively. The iteration states are keep in a pcpu_list_state
> > structure that is passed to the iteration functions.
> >
> > Signed-off-by: Waiman Long<Waiman.Long@xxxxxxx>
> The patch looks good to me now. So you can add:
>
> Reviewed-by: Jan Kara<jack@xxxxxxx>
>
> 								Honza

Thanks for the review.

Cheers,
Longman