From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755130AbZAZVxf (ORCPT ); Mon, 26 Jan 2009 16:53:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752747AbZAZVxZ (ORCPT ); Mon, 26 Jan 2009 16:53:25 -0500 Received: from mx2.redhat.com ([66.187.237.31]:37241 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752471AbZAZVxY (ORCPT ); Mon, 26 Jan 2009 16:53:24 -0500 Date: Mon, 26 Jan 2009 22:50:49 +0100 From: Oleg Nesterov To: Andrew Morton Cc: Ingo Molnar , a.p.zijlstra@chello.nl, rusty@rustcorp.com.au, travis@sgi.com, mingo@redhat.com, davej@redhat.com, cpufreq@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue. Message-ID: <20090126215049.GA3493@redhat.com> References: <20090116191108.533053000@polaris-admin.engr.sgi.com> <20090124001537.7cfde78e.akpm@linux-foundation.org> <200901261711.43943.rusty@rustcorp.com.au> <20090125230130.bcdab2e5.akpm@linux-foundation.org> <20090126171618.GA32091@elte.hu> <20090126103529.cb124a58.akpm@linux-foundation.org> <20090126202022.GA8867@elte.hu> <20090126130046.37b8f34e.akpm@linux-foundation.org> <20090126212727.GA13670@elte.hu> <20090126133551.fab5e27a.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090126133551.fab5e27a.akpm@linux-foundation.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/26, Andrew Morton wrote: > > On Mon, 26 Jan 2009 22:27:27 +0100 > Ingo Molnar wrote: > > > > > * Andrew Morton wrote: > > > > > > So if it's generic it ought to be implemented in a generic way - not a > > > > "dont use from any codepath that has a lock held that might > > > > occasionally also be held in a keventd worklet". (which is a totally > > > > unmaintainable proposition and which would just cause repeat bugs > > > > again and again.) > > > > > > That's different. The core fault here lies in the keventd workqueue > > > handling code. If we're flushing work A then we shouldn't go and block > > > behind unrelated work B. > > > > the blocking is inherent in the concept of "a queue of worklets handled by > > a single thread". > > > > If a worklet is blocked then all other work performed by that thread is > > blocked as well. So by waiting on a piece of work in the queue, we wait > > for all prior work queued up there as well. > > > > The only way to decouple that and to make them independent (and hence > > independently flushable) is to create more parallel flows of execution: > > i.e. by creating another thread (another workqueue). > > > > Nope. As I said, the caller of flush_work() can detach the work item > and run it directly. I am totally confused, just can't understand this thread... I guess, we can't detach and execute because we can run on the different CPU. But "[PATCH 1/3] work_on_cpu: dont try to get_online_cpus() in work_on_cpu." removes get_online_cpus/put_online_cpus, this means the work can run on the wrong CPU anyway. Or work_on_cpu() can hang forever if CPU has already gone away before queue_work_on(). Confused. Oleg.