From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR Date: Thu, 23 Jul 2020 15:04:13 -0400 Message-ID: <6d6279ad-7432-63c1-14c3-18c4cff30bf8@redhat.com> 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=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200723184759.GS119549@hirez.programming.kicks-ass.net> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: peterz@infradead.org Cc: Michael Ellerman , Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, Will Deacon , 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: virtualization@lists.linuxfoundation.org On 7/23/20 2:47 PM, 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. It does add some extra instruction that may slow it down slightly, but I don't agree that it gives nothing back. The cpu lock holder information can be useful in analyzing crash dumps and in some debugging situation. I think it can be useful in RHEL for this readon. How about an x86 config option to allow distros to decide if they want to have it enabled? I will make sure that it will have no performance degradation if the option is not enabled. Cheers, Longman