From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756042AbXLLSCx (ORCPT ); Wed, 12 Dec 2007 13:02:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751993AbXLLSCq (ORCPT ); Wed, 12 Dec 2007 13:02:46 -0500 Received: from phunq.net ([64.81.85.152]:60587 "EHLO moonbase.phunq.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751518AbXLLSCp (ORCPT ); Wed, 12 Dec 2007 13:02:45 -0500 From: Daniel Phillips To: "J. Bruce Fields" Subject: Re: A peek at the future of storage Date: Wed, 12 Dec 2007 10:02:44 -0800 User-Agent: KMail/1.9.5 Cc: linux-kernel@vger.kernel.org References: <200712120846.18320.phillips@phunq.net> <20071212174613.GA16656@fieldses.org> In-Reply-To: <20071212174613.GA16656@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200712121002.44643.phillips@phunq.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 12 December 2007 09:46, J. Bruce Fields wrote: > On Wed, Dec 12, 2007 at 08:46:18AM -0800, Daniel Phillips wrote: > > Incidentally, we ran our tests with 128 knfsd threads. The default > > of 8 threads produces miserable performance on the SSD, which gave > > us a good scare on our initial test run. It would be very nice to > > implement an algorithm to scale the knfsd thread pool > > automatically, in order to eliminate this class of thing that can > > go wrong. If somebody became inspired to take on that little > > project that would be great, otherwise it is in our pipeline for, > > hmm, Christmas delivery. (Exactly which Christmas is left > > unspecified.) > > People have proposed writing a daemon that just reads > /proc/net/rpc/nfsd periodically and uses that to adjust the number of > threads from userspace, probably subject to some limits in a config > file someplace. (Think that could do the job, or is there some reason > this would be easier in the kernel?) I didn't actually say "kernel", though that was what I was thinking, perhaps just out of habit. It seems to me it would be a relatively small change to the existing code, essentially just finishing the idea, without needing to be patched up by userspace. So how would a userspace daemon know that kernel is blocking and new threads are needed? In kernel this is pretty easy: when a new request arrives, look on the thread list and if none are available, generate a new one. Something special needs to be done to handle the case where there are no threads available because they are all piled up on a semaphore due to, for example, somebody unplugging the network cable for a remote disk. We have to avoid generating infinite threads in that case. Ideas? Daniel