linux-kernel - Re: [PATCH v2] fs/nfsd/nfs4callback: Remove deprecated create_singlethread

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Date:   Wed, 09 Nov 2016 08:18:08 -0500
From:   Jeff Layton <jlayton@...chiereds.net>
To:     "J. Bruce Fields" <bfields@...ldses.org>, Tejun Heo <tj@...nel.org>
Cc:     Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs/nfsd/nfs4callback: Remove deprecated
 create_singlethread_workqueue

On Tue, 2016-11-08 at 20:27 -0500, J. Bruce Fields wrote:
> On Tue, Nov 08, 2016 at 05:52:21PM -0500, Tejun Heo wrote:
> > 
> > Hello, Bruce.
> > 
> > On Tue, Nov 08, 2016 at 04:39:11PM -0500, J. Bruce Fields wrote:
> > > 
> > > Apologies, just cleaning out old mail and finding some I should have
> > > responded to long ago:
> > > 
> > > On Wed, Aug 31, 2016 at 02:23:48AM +0530, Bhaktipriya Shridhar wrote:
> > > > 
> > > > The workqueue "callback_wq" queues a single work item &cb->cb_work per
> > > > nfsd4_callback instance and thus, it doesn't require execution ordering.
> > > 
> > > What's "execution ordering"?
> > > 

AIUI, it means that jobs are always run in the order queued and are
serialized.

> > > We definitely do depend on the fact that at most one of these is running
> > > at a time.
> > 

We do?

> > If there can be multiple cb's and thus cb->cb_work's per callback_wq,
> > it'd need explicit ordering.  Is that the case?
> 

These are basically client RPC tasks, and the cb_work just handles the
submission into the client RPC state machine. Just because we're running
several callbacks at the same time doesn't mean that they need to be
strictly ordered. The client state machine can certainly handle running
these in parallel.

> Yes, there can be multiple cb_work's.
> 

Yes, but each is effectively a separate work unit. I see no reason why
we'd need to order them at all.

-- 
Jeff Layton <jlayton@...chiereds.net>