From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750819AbXBND3A (ORCPT ); Tue, 13 Feb 2007 22:29:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750820AbXBND3A (ORCPT ); Tue, 13 Feb 2007 22:29:00 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:4697 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbXBND3A (ORCPT ); Tue, 13 Feb 2007 22:29:00 -0500 X-AuthUser: davidel@xmailserver.org Date: Tue, 13 Feb 2007 19:28:56 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Ingo Molnar cc: Linux Kernel Mailing List , Linus Torvalds , Arjan van de Ven , Christoph Hellwig , Andrew Morton , Alan Cox , Ulrich Drepper , Zach Brown , Evgeniy Polyakov , "David S. Miller" , Benjamin LaHaise , Suparna Bhattacharya , Thomas Gleixner Subject: Re: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support In-Reply-To: <20070213142010.GA638@elte.hu> Message-ID: References: <20070213142010.GA638@elte.hu> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 13 Feb 2007, Ingo Molnar wrote: > I'm pleased to announce the first release of the "Syslet" kernel feature > and kernel subsystem, which provides generic asynchrous system call > support: > [...] Ok, I had little to time review the code, but it has been a long working day, so bear with me if I missed something. I don't see how sys_async_exec would not block, based on your patches. Let's try to follow: - We enter sys_async_exec - We may fill the pool, but that's nothing interesting ATM. A bunch of threads will be created, and they'll end up sleeping inside the cachemiss_loop - We set the async_ready pointer and we fall inside exec_atom - There we copy the atom (nothing interesting from a scheduling POV) and we fall inside __exec_atom - In __exec_atom we do the actual syscall call. Note that we're still the task/thread that called sys_async_exec - So we enter the syscall, and now we end up in schedule because we're just unlucky - We notice that the async_ready pointer is not NULL, and we call __async_schedule - Finally we're in pick_new_async_thread and we pick one of the ready threads sleeping in cachemiss_loop - We copy the pt_regs to the newly picked-up thread, we set its async head pointer, we set the current task async_ready pointer to NULL, we re-initialize the async_thread structure (the old async_ready), and we put ourselves in the busy_list - Then we roll back to the schedule that started everything, and being still "prev" for the scheduler, we go to sleep So the sys_async_exec task is going to block. Now, am I being really tired, or the cachemiss fast return is simply not there? There's another problem AFAICS: - We woke up one of the cachemiss_loop threads in pick_new_async_thread - The threads wakes up, mark itself as busy, and look at the ->work pointer hoping to find something to work on But we never set that pointer to a userspace atom AFAICS. Me blind? :) - Davide