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

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Message-ID: <570FE5E7.5000004@hpe.com>
Date:	Thu, 14 Apr 2016 14:48:07 -0400
From:	Waiman Long <waiman.long@....com>
To:	Jan Kara <jack@...e.cz>
CC:	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <dchinner@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH v7 1/4] lib/percpu-list: Per-cpu list with associated
 per-cpu locks

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@....com>
> The patch looks good to me now. So you can add:
>
> Reviewed-by: Jan Kara<jack@...e.cz>
>
> 								Honza

Thanks for the review.

Cheers,
Longman