From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR Date: Fri, 24 Jul 2020 09:16:48 +0100 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 Return-path: Content-Disposition: inline In-Reply-To: <20200723184759.GS119549@hirez.programming.kicks-ass.net> Sender: kvm-ppc-owner@vger.kernel.org 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 List-Id: linux-arch.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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 Date: Fri, 24 Jul 2020 09:16:48 +0100 From: Will Deacon 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> Sender: linux-arch-owner@vger.kernel.org List-ID: 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 Message-ID: <20200724081648._yjeS6L27IfaD_uzUIBeN7mVLXdZ6PiC6GZTvFAuy68@z> 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