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([2601:188:c100:5710:315f:57b3:b997:5fca]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4796ed9bcc3sm9426491cf.63.2025.04.10.07.35.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Apr 2025 07:35:55 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <77988036-7550-4ee2-a738-9f9bd4417001@redhat.com> Date: Thu, 10 Apr 2025 10:35:55 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] timers: Exclude isolated cpus from timer migation To: Frederic Weisbecker , Gabriele Monaco Cc: Thomas Gleixner , linux-kernel@vger.kernel.org References: <20250410065446.57304-2-gmonaco@redhat.com> <87ecy0tob1.ffs@tglx> <2c9d71fd79d7d1cec66e48bcb87b39a874858f01.camel@redhat.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/10/25 9:03 AM, Frederic Weisbecker wrote: > Le Thu, Apr 10, 2025 at 12:38:25PM +0200, Gabriele Monaco a écrit : >> On Thu, 2025-04-10 at 10:26 +0200, Thomas Gleixner wrote: >>> How can that happen? There is always at least _ONE_ housekeeping, >>> non-isolated, CPU online, no? >>> >> In my understanding it shouldn't, but I'm not sure there's anything >> preventing the user from isolating everything via cpuset. >> Anyway that's something no one in their mind should do, so I guess I'd >> just opt for the cpumask_first (or actually cpumask_any, like before >> the change). > With "nohz_full=..." or "isolcpus=nohz,..." there is always at least one > housekeeping CPU. But with isolcpus=[domain] or cpusets equivalents > (v1 cpuset.sched_load_balance, v2 isolated partion) there is nothing that > prevents all CPUs from being isolated. Actually v2 won't allow users to isolate all the CPUs. Users can probably do that with v1's cpuset.sched_load_balance. Cheers, Longman