From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jan Kara <jack@suse.com>, Jeff Layton <jlayton@poochiereds.net>,
"J. Bruce Fields" <bfields@fieldses.org>,
Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux-foundation.org>,
<linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Andi Kleen <andi@firstfloor.org>,
Dave Chinner <dchinner@redhat.com>,
Scott J Norton <scott.norton@hp.com>,
Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [RFC PATCH 1/2] lib/percpu-list: Per-cpu list with associated per-cpu locks
Date: Wed, 17 Feb 2016 11:16:10 -0500 [thread overview]
Message-ID: <56C49CCA.7090805@hpe.com> (raw)
In-Reply-To: <20160217110520.GN6375@twins.programming.kicks-ass.net>
On 02/17/2016 06:05 AM, Peter Zijlstra wrote:
> On Wed, Feb 17, 2016 at 12:00:40PM +0100, Peter Zijlstra wrote:
>> On Wed, Feb 17, 2016 at 08:53:18PM +1100, Dave Chinner wrote:
>>>> +/**
>>>> + * for_all_percpu_list_entries - iterate over all the per-cpu list with locking
> But the locking is 'pointless'. You only lock one per-cpu sublist at a
> time, therefore the list can be modified concurrently anyhow.
For each per-cpu list, there can be only 1 task allowed to make changes.
If you are talking about all the per-cpu lists within the group,
operations can happen in parallel.
> So why not use RCU for the list iteration and avoid potentially large
> lock hold times?
>
I know we can use RCU for singly linked list, but I don't think we can
use that for doubly linked list as there is no easy way to make atomic
changes to both prev and next pointers simultaneously unless you are
taking about 16b cmpxchg which is only supported in some architecture.
Cheers,
Longman
next prev parent reply other threads:[~2016-02-17 16:16 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-17 1:31 [RFC PATCH 0/2] vfs: Use per-cpu list for SB's s_inodes list Waiman Long
2016-02-17 1:31 ` [RFC PATCH 1/2] lib/percpu-list: Per-cpu list with associated per-cpu locks Waiman Long
2016-02-17 9:53 ` Dave Chinner
2016-02-17 11:00 ` Peter Zijlstra
2016-02-17 11:05 ` Peter Zijlstra
2016-02-17 16:16 ` Waiman Long [this message]
2016-02-17 16:22 ` Peter Zijlstra
2016-02-17 16:27 ` Christoph Lameter
2016-02-17 17:12 ` Waiman Long
2016-02-17 17:18 ` Peter Zijlstra
2016-02-17 17:41 ` Waiman Long
2016-02-17 18:22 ` Peter Zijlstra
2016-02-17 18:45 ` Waiman Long
2016-02-17 19:39 ` Peter Zijlstra
2016-02-17 11:10 ` Dave Chinner
2016-02-17 11:26 ` Peter Zijlstra
2016-02-17 11:36 ` Peter Zijlstra
2016-02-17 15:56 ` Waiman Long
2016-02-17 16:02 ` Peter Zijlstra
2016-02-17 15:13 ` Christoph Lameter
2016-02-17 1:31 ` [RRC PATCH 2/2] vfs: Use per-cpu list for superblock's inode list Waiman Long
2016-02-17 7:16 ` Ingo Molnar
2016-02-17 15:40 ` Waiman Long
2016-02-17 10:37 ` Dave Chinner
2016-02-17 16:08 ` Waiman Long
2016-02-18 23:58 ` [RFC PATCH 0/2] vfs: Use per-cpu list for SB's s_inodes list Dave Chinner
2016-02-19 21:04 ` Long, Wai Man
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56C49CCA.7090805@hpe.com \
--to=waiman.long@hpe.com \
--cc=andi@firstfloor.org \
--cc=bfields@fieldses.org \
--cc=cl@linux-foundation.org \
--cc=david@fromorbit.com \
--cc=dchinner@redhat.com \
--cc=doug.hatch@hp.com \
--cc=jack@suse.com \
--cc=jlayton@poochiereds.net \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=scott.norton@hp.com \
--cc=tj@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.