From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 408F0C4332B for ; Wed, 18 Mar 2020 22:28:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 200FD20772 for ; Wed, 18 Mar 2020 22:28:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727174AbgCRW2z (ORCPT ); Wed, 18 Mar 2020 18:28:55 -0400 Received: from ale.deltatee.com ([207.54.116.67]:55828 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726663AbgCRW2z (ORCPT ); Wed, 18 Mar 2020 18:28:55 -0400 Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.92) (envelope-from ) id 1jEhAx-0000sH-OT; Wed, 18 Mar 2020 16:28:36 -0600 To: Thomas Gleixner , LKML Cc: Peter Zijlstra , Linus Torvalds , Ingo Molnar , Will Deacon , "Paul E . McKenney" , Joel Fernandes , Steven Rostedt , Randy Dunlap , Arnd Bergmann , Sebastian Andrzej Siewior , Kurt Schwemmer , Bjorn Helgaas , linux-pci@vger.kernel.org, Felipe Balbi , Greg Kroah-Hartman , linux-usb@vger.kernel.org, Kalle Valo , "David S. Miller" , linux-wireless@vger.kernel.org, netdev@vger.kernel.org, Oleg Nesterov , Davidlohr Bueso , Michael Ellerman , linuxppc-dev@lists.ozlabs.org References: <20200318204302.693307984@linutronix.de> <20200318204408.521507446@linutronix.de> From: Logan Gunthorpe Message-ID: <9bb6db07-12c4-c272-3a98-baed2ac2f738@deltatee.com> Date: Wed, 18 Mar 2020 16:28:34 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200318204408.521507446@linutronix.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, dave@stgolabs.net, oleg@redhat.com, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, davem@davemloft.net, kvalo@codeaurora.org, linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, balbi@kernel.org, linux-pci@vger.kernel.org, bhelgaas@google.com, kurt.schwemmer@microsemi.com, bigeasy@linutronix.de, arnd@arndb.de, rdunlap@infradead.org, rostedt@goodmis.org, joel@joelfernandes.org, paulmck@kernel.org, will@kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, peterz@infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [patch V2 11/15] completion: Use simple wait queues X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 2020-03-18 2:43 p.m., Thomas Gleixner wrote: > There is no semantical or functional change: > > - completions use the exclusive wait mode which is what swait provides > > - complete() wakes one exclusive waiter > > - complete_all() wakes all waiters while holding the lock which protects > the wait queue against newly incoming waiters. The conversion to swait > preserves this behaviour. > > complete_all() might cause unbound latencies with a large number of waiters > being woken at once, but most complete_all() usage sites are either in > testing or initialization code or have only a really small number of > concurrent waiters which for now does not cause a latency problem. Keep it > simple for now. Seems like it would be worth adding a note for this to the complete_all() doc string. Otherwise developers will not likely find out about this issue and may not keep it as simple as you'd like. Logan