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=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,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 6C99FC43387 for ; Wed, 2 Jan 2019 18:11:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 434F7218EA for ; Wed, 2 Jan 2019 18:11:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="nA3v0Op+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727267AbfABSKz (ORCPT ); Wed, 2 Jan 2019 13:10:55 -0500 Received: from mail-it1-f195.google.com ([209.85.166.195]:40545 "EHLO mail-it1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727192AbfABSKz (ORCPT ); Wed, 2 Jan 2019 13:10:55 -0500 Received: by mail-it1-f195.google.com with SMTP id h193so39710354ita.5 for ; Wed, 02 Jan 2019 10:10:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=ULtSJ1U05vNUljckl2z7wbeqdVpCxUWiFv5LN7nAdIM=; b=nA3v0Op+y7PBkwCMo6fSTnvJPS0mdHs+SKcmH2dEqiRBGbLIQUrM4CelsSeS6jM+NM Nq6gwL05B8nuvaA5noqlrnZG6tv1ErD44KDX6dE7lcXHk5eQYYsPsgBgDoQB6s4IUzv3 +lcqZCDJo9EpRwSWEazKfvD5FtcSkF95+JBnXuBOlRe0x2dPE3YQCv+H+mIfDCeNigzX 0yYwYg2Ig4pHRIsuS2RIYxpFVFsHp8A+rjzn8uZbPHMBuHNJIAEgVTnnzTrh7rcxq2w5 posU1MkLj1ZKe7i3oFzzlu33ggyGSuAL1rZcGZhbLsgFJzQTpVOVFn7vuOttvUUQNSMc rlUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=ULtSJ1U05vNUljckl2z7wbeqdVpCxUWiFv5LN7nAdIM=; b=ujc7N6R23tKKMFQCK52/HqlIagHcQkoK7sni3UoeNK2kbPuXqPn1OANuv8AtIJbFA4 BEsPcJVa7hoc+tYK5xRzrSGxeC/m2x0ULZeGwaVWuEyWYbI+JFMY8jrc21iBJ9AbFnWB +4IjgHJeRAURDaNZ3jfFmdIIroEKct8IbNQkQFw/wVc+TMdGxMBeda2CyBysUmAp+bIm 9grEQGdrSXJnKUD7n4nKmOKzLNUeadH3Z7yikZLxgaT/Kuhz1X9ckUAZj+LXNnjPD3ge TlcRhJ/XolWbpMlTU21IVzdbW6Vyq64zqqmr5HvRrZfRJN+KHSNRMLI668BA58LO/6ad q3FQ== X-Gm-Message-State: AA+aEWZvRX52dtzuM/QP6ugkeg+HroQgX2pOaJ1tmkZCKa0hEADLgobG RXDrl8NrfGjkNXumnQ/+MrqbK5DcbuhyAg== X-Google-Smtp-Source: AFSGD/UCEr7e3GE7B3Y5g7wxij9edGj1mbKogV04tq+6Ayln2TJ7oHgJfuFb0blb0EiqN23ehY+xTQ== X-Received: by 2002:a05:660c:128c:: with SMTP id s12mr22655901ita.145.1546452654112; Wed, 02 Jan 2019 10:10:54 -0800 (PST) Received: from [192.168.1.56] ([216.160.245.98]) by smtp.gmail.com with ESMTPSA id v3sm7170302ioj.79.2019.01.02.10.10.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 02 Jan 2019 10:10:53 -0800 (PST) Subject: Re: block: only use __set_current_state() for polled IO To: Linus Torvalds Cc: "linux-block@vger.kernel.org" , Christoph Hellwig References: <181e0aa7-34a5-5445-70b2-45770a81659d@kernel.dk> From: Jens Axboe Message-ID: <0734f570-f9f7-f775-84d5-3ed22388e3c0@kernel.dk> Date: Wed, 2 Jan 2019 11:10:52 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 1/2/19 11:07 AM, Linus Torvalds wrote: > On Wed, Jan 2, 2019 at 9:55 AM Jens Axboe wrote: >> >> A previous commit deemed it safe to use __set_current_state() for IRQ >> driven O_DIRECT, but that's isn't necessarily the case. Be safer and >> only apply that optimization to polled IO, where we know the the task is >> going to find the completions itself. > > No. > > We're just reverting 849a370016a5. > > There is absolutely no point in trying to avoid a memory barrier that > is maybe 15 CPU cycles. > > Stop this craziness. The optimization is garbage. If you want to save > 15 cycles, get rid of code, don't add new code in an area where the > block maintainers have already shown that they can't get it right. Fine, we'll just revert the damn thing then. -- Jens Axboe