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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 03638C433E1 for ; Fri, 24 Jul 2020 08:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D1EDA20748 for ; Fri, 24 Jul 2020 08:16:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595578615; bh=MtSSJVr7CkQ6qYnldFXBBhVSH/FImYJYfT41DnqnyfQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=fK8yQKgyia7CHOYzyQSvjuVRdCDZbciXYaxBDMW9QeLjl3wz+R6bKP3Nv4pIIjkOi n7xsX7rDgV1vfiZ5ONnnMAL82Ys2ty016HaL5I0M0CBGTzYvpWT0qkRGNqUPfgjE8b fvlQaQwTa9dIcNBzrAGP4wplZ2/RDtCS2bEVMhCo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726952AbgGXIQy (ORCPT ); Fri, 24 Jul 2020 04:16:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:50670 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726437AbgGXIQx (ORCPT ); Fri, 24 Jul 2020 04:16:53 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 776FE2074A; Fri, 24 Jul 2020 08:16:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595578613; bh=MtSSJVr7CkQ6qYnldFXBBhVSH/FImYJYfT41DnqnyfQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RwKzdNIM0IbM4QhStWrpabxkbmQfmemxolOJQbQ35i0L7IjfMB2mLxbxDs3yf9OMG t5gjDHgkaIcsKKrEcDnxZ3E6OOSzQ0tacBMUiHRqwCuYIXYMIMsfdvbx+wenpuiypB b+V/llaOX/7WR8IKO4GbceZdbj7sGKlc3q02Gn3Q= Date: Fri, 24 Jul 2020 09:16:48 +0100 From: Will Deacon To: peterz@infradead.org Cc: Waiman Long , 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 Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR Message-ID: <20200724081647.GA16642@willie-the-truck> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200723184759.GS119549@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. Will