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[34.123.190.156]) by smtp.gmail.com with ESMTPSA id i15-20020a02cc4f000000b0039deb26853csm3800016jaq.10.2023.08.30.03.18.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Aug 2023 03:18:34 -0700 (PDT) Date: Wed, 30 Aug 2023 10:18:33 +0000 From: Joel Fernandes To: Huacai Chen Cc: paulmck@kernel.org, Thomas Gleixner , Z qiang , Huacai Chen , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Ingo Molnar , John Stultz , Stephen Boyd , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Sergey Senozhatsky , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Binbin Zhou Subject: Re: [PATCH V4 2/2] rcu: Update jiffies in rcu_cpu_stall_reset() Message-ID: <20230830101833.GA310377@google.com> References: <2681134d-cc88-49a0-a1bc-4ec0816288f6@paulmck-laptop> <20230828133348.GA1553000@google.com> <142b4bff-6a2e-4ea0-928c-3cfe9befa403@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Aug 30, 2023 at 12:25:56PM +0800, Huacai Chen wrote: > On Tue, Aug 29, 2023 at 10:46 PM Joel Fernandes wrote: > > > > On Tue, Aug 29, 2023 at 12:08 AM Huacai Chen wrote: > > > > > > Hi, Joel, > > > > > > On Tue, Aug 29, 2023 at 4:47 AM Joel Fernandes wrote: > > > > > > > > Hi Huacai, > > > > > > > > On Mon, Aug 28, 2023 at 11:13 AM Huacai Chen wrote: > > > > > > > > > [...] > > > > > > > > > > > > > [Huacai] > > > > > > > I also think the original patch should be OK, but I have another > > > > > > > question: what will happen if the current GP ends before > > > > > > > nr_fqs_jiffies_stall reaches zero? > > > > > > > > > > > > Nothing should happen. Stall detection only happens when a GP is in > > > > > > progress. If a new GP starts, it resets nr_fqs_jiffies_stall. > > > > > > > > > > > > Or can you elaborate your concern more? > > > > > OK, I will test your patch these days. Maybe putting > > > > > nr_fqs_jiffies_stall before jiffies_force_qs is better, because I > > > > > think putting an 'int' between two 'long' is wasting space. :) > > > > > > > > That's a good point and I'll look into that. > > > Another point, is it better to replace ULONG_MAX with ULONG_MAX/4 as > > > Paul suggested? > > > > > > > I could do that but I don't feel too strongly about it. I will keep it > > at ULONG_MAX if it's OK with everyone. > > > > > > Meanwhile I pushed the patch out to my 6.4 stable tree for testing on my fleet. > > > > > > > > Ideally, I'd like to change the stall detection test in the rcutorture > > > > to actually fail rcutorture if stalls don't happen in time. But at > > > > least I verified this manually using rcutorture. > > > > > > > > I should also add a documentation patch for stallwarn.rst to document > > > > the understandable sensitivity of RCU stall detection to jiffies > > > > updates (or lack thereof). Or if you have time, I'd appreciate support > > > > on such a patch (not mandatory but I thought it would not hurt to > > > > ask). > > > > > > > > Looking forward to how your testing goes as well! > > > I have tested, it works for KGDB. > > > > Thanks! If you don't mind, I will add your Tested-by tag to the patch > > and send it out soon. My tests also look good! > > You can add my Tested-by, but Reported-by should be "Binbin Zhou > " Thanks, if/when Paul takes it, he could kindly change the Reported-by, or I could. thanks, - Joel