On Wed, 2016-11-09 at 15:08 +0000, Trond Myklebust wrote: > On Wed, 2016-11-09 at 08:18 -0500, Jeff Layton wrote: > > > > 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. > > > > There needs to be serialisation at the session level (i.e. the > callbacks have to respect the slot limits set by the client) however > there shouldn’t be a need for serialisation at the RPC level. > > Cheers > Trond Yes, that all happens in nfsd4_cb_prepare, which is the rpc_call_prepare operation for the callback. That gets run by the rpc state machine in the context of the rpciod workqueues. None of that happens in the context of the cb_work here. If you have a look at nfsd4_run_cb_work, you can see that it just does a cb_ops->prepare and then submits it to the client rpc engine with rpc_call_async. None of that should require singlethreaded workqueue semantics. -- Jeff Layton <jlayton@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
