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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 E132FC46470 for ; Tue, 7 Aug 2018 16:04:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9CF5E21885 for ; Tue, 7 Aug 2018 16:04:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9CF5E21885 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389091AbeHGSTl (ORCPT ); Tue, 7 Aug 2018 14:19:41 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:42524 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726419AbeHGSTl (ORCPT ); Tue, 7 Aug 2018 14:19:41 -0400 Received: from localhost.localdomain (c-24-4-125-7.hsd1.ca.comcast.net [24.4.125.7]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 61D35BC6; Tue, 7 Aug 2018 16:04:42 +0000 (UTC) Date: Tue, 7 Aug 2018 09:04:41 -0700 From: Andrew Morton To: Christoph Hellwig Cc: viro@zeniv.linux.org.uk, Avi Kivity , Linus Torvalds , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/4] aio: allow direct aio poll comletions for keyed wakeups Message-Id: <20180807090441.67f7e281f502ce448de849c1@linux-foundation.org> In-Reply-To: <20180807072555.GA678@lst.de> References: <20180806083058.14724-1-hch@lst.de> <20180806083058.14724-5-hch@lst.de> <20180806152705.37809e16c02543cc24626607@linux-foundation.org> <20180807072555.GA678@lst.de> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 7 Aug 2018 09:25:55 +0200 Christoph Hellwig wrote: > On Mon, Aug 06, 2018 at 03:27:05PM -0700, Andrew Morton wrote: > > On Mon, 6 Aug 2018 10:30:58 +0200 Christoph Hellwig wrote: > > > > > If we get a keyed wakeup for a aio poll waitqueue and wake can acquire the > > > ctx_lock without spinning we can just complete the iocb straight from the > > > wakeup callback to avoid a context switch. > > > > Why do we try to avoid spinning on the lock? > > Because we are called with the lock on the waitqueue called, which > nests inside it. Ah. > > > + /* try to complete the iocb inline if we can: */ > > > > ie, this comment explains 'what" but not "why". > > > > (There's a typo in Subject:, btw) > > Because it is faster obviously. I can update the comment. I meant the comment could explain why it's a trylock instead of a spin_lock().