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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4bda15f59besm77848421cf.8.2025.09.22.14.59.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Sep 2025 14:59:13 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <1c77c072-ddf1-4894-a5bb-73bf13a838b9@redhat.com> Date: Mon, 22 Sep 2025 17:59:12 -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 19/33] sched/isolation: Remove HK_TYPE_TICK test from cpu_is_isolated() To: Frederic Weisbecker , Waiman Long Cc: LKML , Ingo Molnar , Marco Crivellari , Michal Hocko , Peter Zijlstra , Tejun Heo , Thomas Gleixner , Vlastimil Babka References: <20250829154814.47015-1-frederic@kernel.org> <20250829154814.47015-20-frederic@kernel.org> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/22/25 11:19 AM, Frederic Weisbecker wrote: > Le Tue, Sep 02, 2025 at 10:28:58AM -0400, Waiman Long a écrit : >> On 8/29/25 11:48 AM, Frederic Weisbecker wrote: >>> It doesn't make sense to use nohz_full without also isolating the >>> related CPUs from the domain topology, either through the use of >>> isolcpus= or cpuset isolated partitions. >>> >>> And now HK_TYPE_DOMAIN includes all kinds of domain isolated CPUs. >>> >>> This means that HK_TYPE_KERNEL_NOISE (of which HK_TYPE_TICK is only an >>> alias) is always a superset of HK_TYPE_DOMAIN. >> That may not be true. Users can still set "isolcpus=" and "nohz_full=" with >> disjoint set of CPUs whether cpuset is used for additional isolated CPUs or >> not. > There can be domain isolated CPU that are not nohz_full indeed. But OTOH nohz_full > CPUs that are not domain isolated don't make much sense. I know such settings > exist but it's usually a half working misconfiguration. I wish I had > forbidden that since the early days but this was from times when we didn't know > about all the potential usages. The assumption is true for cpuset isolated partition, but users may still set conflicting nohz_full and isolcpus parameters by mistake. We should probably a warning if this happens and document that clearly to enforce such rule. Cheers, Longman