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 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 BAAEBC43218 for ; Mon, 29 Apr 2019 00:27:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8EDDF20675 for ; Mon, 29 Apr 2019 00:27:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726893AbfD2A15 (ORCPT ); Sun, 28 Apr 2019 20:27:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44566 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726223AbfD2A14 (ORCPT ); Sun, 28 Apr 2019 20:27:56 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 524F081F0F; Mon, 29 Apr 2019 00:27:56 +0000 (UTC) Received: from llong.remote.csb (ovpn-120-22.rdu2.redhat.com [10.10.120.22]) by smtp.corp.redhat.com (Postfix) with ESMTP id D91764A3; Mon, 29 Apr 2019 00:27:54 +0000 (UTC) Subject: Re: [PATCH-tip v7 00/20] locking/rwsem: Rwsem rearchitecture part 2 To: Linus Torvalds Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" , Linux List Kernel Mailing , the arch/x86 maintainers , Davidlohr Bueso , Tim Chen , huang ying References: <20190428212557.13482-1-longman@redhat.com> <3f8fd44d-1962-e309-49b5-bb16fd662312@redhat.com> From: Waiman Long Organization: Red Hat Message-ID: <604c8751-5269-de29-0b7f-b3e93b6df4ca@redhat.com> Date: Sun, 28 Apr 2019 20:27:54 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 29 Apr 2019 00:27:56 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/28/19 8:10 PM, Linus Torvalds wrote: > On Sun, Apr 28, 2019 at 4:12 PM Waiman Long wrote: >> I implemented your suggestion in patch 1 as it will produce simpler and >> faster code. However, one of the changes in my patchset is to wake up >> all the readers in the wait list. This means I have to jump over the >> writers and wake up the readers behind them as well. See patch 11 for >> details. As a result, I have to revert back to use list_add_tail() and >> list_for_each_entry_safe() for the first pass. That is why the diff for >> the whole patchset is just the below change. It is done on purpose, not >> an omission. > Ahh, ok. In that case I suspect the clever code isn't even worth it, > since it very much depends on just splitting the list in a fixed > place. > > Linus Not really, this is a serious problem that have to be backported to earlier stable releases and downstream. The clever code is helpful in those cases. Cheers, Longman