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=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 3E827C433E3 for ; Fri, 24 Jul 2020 19:11:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1654A206F0 for ; Fri, 24 Jul 2020 19:11:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RHVnsO9D" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726782AbgGXTLJ (ORCPT ); Fri, 24 Jul 2020 15:11:09 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:60789 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726512AbgGXTLI (ORCPT ); Fri, 24 Jul 2020 15:11:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595617867; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/IKeY6oErXCv4WxvHD12K0X54wE8JqQGDnTdTiMdbbI=; b=RHVnsO9D2LL8J0m5E/jkUjUIKWBgw/m3Jc2H/4rcNXDt7kkS5hX3+Buv7rewneUbKzgNNL rR4cDCplwVwqSLjF+V2K1NvBv+k5OEQLWQLa9b84/cRS8XR9yw/BQ5jL8DF8PHJRsPTDe2 xS5NwySHsx2VWdcIXe45AYvcSw0rnjg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-114-KSQWmsA2MWyLHLlGSd4LFQ-1; Fri, 24 Jul 2020 15:11:03 -0400 X-MC-Unique: KSQWmsA2MWyLHLlGSd4LFQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A0ADD8015F4; Fri, 24 Jul 2020 19:11:01 +0000 (UTC) Received: from llong.remote.csb (ovpn-117-203.rdu2.redhat.com [10.10.117.203]) by smtp.corp.redhat.com (Postfix) with ESMTP id 572FD1A835; Fri, 24 Jul 2020 19:11:00 +0000 (UTC) Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR To: Will Deacon , peterz@infradead.org Cc: Michael Ellerman , Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, Boqun Feng , Ingo Molnar , Anton Blanchard , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org References: <20200706043540.1563616-1-npiggin@gmail.com> <20200706043540.1563616-6-npiggin@gmail.com> <874kqhvu1v.fsf@mpe.ellerman.id.au> <8265d782-4e50-a9b2-a908-0cb588ffa09c@redhat.com> <20200723140011.GR5523@worktop.programming.kicks-ass.net> <845de183-56f5-2958-3159-faa131d46401@redhat.com> <20200723184759.GS119549@hirez.programming.kicks-ass.net> <20200724081647.GA16642@willie-the-truck> From: Waiman Long Organization: Red Hat Message-ID: <8532332b-85dd-661b-cf72-81a8ceb70747@redhat.com> Date: Fri, 24 Jul 2020 15:10:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200724081647.GA16642@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/24/20 4:16 AM, Will Deacon wrote: > On Thu, Jul 23, 2020 at 08:47:59PM +0200, peterz@infradead.org wrote: >> On Thu, Jul 23, 2020 at 02:32:36PM -0400, Waiman Long wrote: >>> BTW, do you have any comment on my v2 lock holder cpu info qspinlock patch? >>> I will have to update the patch to fix the reported 0-day test problem, but >>> I want to collect other feedback before sending out v3. >> I want to say I hate it all, it adds instructions to a path we spend an >> aweful lot of time optimizing without really getting anything back for >> it. >> >> Will, how do you feel about it? > I can see it potentially being useful for debugging, but I hate the > limitation to 256 CPUs. Even arm64 is hitting that now. After thinking more about that, I think we can use all the remaining bits in the 16-bit locked_pending. Reserving 1 bit for locked and 1 bit for pending, there are 14 bits left. So as long as NR_CPUS < 16k (requirement for 16-bit locked_pending), we can put all possible cpu numbers into the lock. We can also just use smp_processor_id() without additional percpu data. > > Also, you're talking ~1% gains here. I think our collective time would > be better spent off reviewing the CNA series and trying to make it more > deterministic. I thought you guys are not interested in CNA. I do want to get CNA merged, if possible. Let review the current version again and see if there are ways we can further improve it. Cheers, Longman