Return-Path: linux-kernel-owner@vger.kernel.org MIME-Version: 1.0 In-Reply-To: <20141203142034.5c14529d@tlielax.poochiereds.net> References: <1417544663-13299-1-git-send-email-jlayton@primarydata.com> <20141203121118.21a32fe1@notabene.brown> <20141202202946.1e0f399b@tlielax.poochiereds.net> <20141203155649.GB5013@htj.dyndns.org> <20141203110405.5ecc85df@tlielax.poochiereds.net> <20141203140202.7865bedb@tlielax.poochiereds.net> <20141203142034.5c14529d@tlielax.poochiereds.net> Date: Wed, 3 Dec 2014 14:59:43 -0500 Message-ID: Subject: Re: [RFC PATCH 00/14] nfsd/sunrpc: add support for a workqueue-based nfsd From: Trond Myklebust To: Jeff Layton Cc: Tejun Heo , NeilBrown , Linux NFS Mailing List , Linux Kernel mailing list , Al Viro Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: On Wed, Dec 3, 2014 at 2:20 PM, Jeff Layton wrote: > On Wed, 3 Dec 2014 14:08:01 -0500 > Trond Myklebust wrote: >> Which workqueue are you using? Since the receive code is non-blocking, >> I'd expect you might be able to use rpciod, for the initial socket >> reads, but you wouldn't want to use that for the actual knfsd >> processing. >> > > I'm using the same (nfsd) workqueue for everything. The workqueue > isn't really the bottleneck though, it's the work_struct. > > Basically, the problem is that the work_struct in the svc_xprt was > remaining busy for far too long. So, even though the XPT_BUSY bit had > cleared, the work wouldn't get picked up again until the previous > workqueue job had returned. > > With the change I made today, I just added a new work_struct to > svc_rqst and queue that to the same workqueue to do svc_process as soon > as the receive is done. That means though that each RPC ends up waiting > in the queue twice (once to do the receive and once to process the > RPC), and I think that's probably the reason for the performance delta. Why would the queuing latency still be significant now? > What I think I'm going to do on the next pass is have the job that > enqueues the xprt instead try to find an svc_rqst. If it finds it, > then it can go ahead and queue the work struct in it to do the receive > and processing in a single go. > > If it can't find one, it'll queue the xprt's work to allocate one and > then queue that to do all of the work as before. That will likely > penalize the case where there isn't an available svc_rqst, but in the > common case that there is one it should go quickly. -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@primarydata.com