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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 548D2C46470 for ; Tue, 7 Aug 2018 07:20:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 13E87219CB for ; Tue, 7 Aug 2018 07:20:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 13E87219CB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de 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 S2388867AbeHGJdh (ORCPT ); Tue, 7 Aug 2018 05:33:37 -0400 Received: from verein.lst.de ([213.95.11.211]:59646 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727360AbeHGJdg (ORCPT ); Tue, 7 Aug 2018 05:33:36 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id F0C6B68D62; Tue, 7 Aug 2018 09:25:55 +0200 (CEST) Date: Tue, 7 Aug 2018 09:25:55 +0200 From: Christoph Hellwig To: Andrew Morton Cc: Christoph Hellwig , 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: <20180807072555.GA678@lst.de> References: <20180806083058.14724-1-hch@lst.de> <20180806083058.14724-5-hch@lst.de> <20180806152705.37809e16c02543cc24626607@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180806152705.37809e16c02543cc24626607@linux-foundation.org> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > + /* 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.