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[213.44.135.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8dc21e7sm21119219f8f.36.2025.07.17.09.32.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Jul 2025 09:32:27 -0700 (PDT) From: Valentin Schneider To: Frederic Weisbecker , LKML Cc: Frederic Weisbecker , Andrew Morton , Ingo Molnar , Marcelo Tosatti , Michal Hocko , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Vlastimil Babka , linux-mm@kvack.org Subject: Re: [PATCH 4/6] tick/nohz: Move nohz_full related fields out of hot task struct's places In-Reply-To: <20250703140717.25703-5-frederic@kernel.org> References: <20250703140717.25703-1-frederic@kernel.org> <20250703140717.25703-5-frederic@kernel.org> Date: Thu, 17 Jul 2025 18:32:26 +0200 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Cv8yC1APu2N4ot-nObzhfAT_AOXKQOX-9QO462D6bME_1752769950 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Stat-Signature: 89fxdc34a3hkstgzzzdhkkmks77abgxs X-Rspamd-Queue-Id: 2464E180016 X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1752769953-508068 X-HE-Meta: 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 SxQqfrVI hO6RUzrXTw3xQdApQvMbJzmYs1Tm3kU/ucqUaRfJY+JcJ/r7mS8pkpzeudhuf2ors0lhs6rIBQy17VhnBZEBfQBTb4frqrxdOVlglVe69k7les/TOy3mnldZw3WpgSgpmntrUEZ0Gk3NlVyLrJqeCHry5nC/VOFVbEwSVf7wItypG6JEk0cQ/uji7Cv0lFDzyPu6wTT/6D7wTYTF848G6x5hiJEk/4iJ80f3voQGt6iCnQ0vMMdck4VDFSVWVA5MV4760X+LLx5Rts/mIIMn5uQEOoaimK1Mv/z3NzAEhIMqbO/OJC70wEOnGOqRaVKim2n1KEYW802fpBeobgcasKXWqtVDmA1ukm9uspa9dJ9jWyRbN09wnxsf2DucuNoFtuFL9CULRLoXLYR2B5HrlV07Hv2wT72yXQ/vb X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 03/07/25 16:07, Frederic Weisbecker wrote: > nohz_full is a feature that only fits into rare and very corner cases. > Yet distros enable it by default and therefore the related fields are > always reserved in the task struct. > > Those task fields are stored in the middle of cacheline hot places such > as cputime accounting and context switch counting, which doesn't make > any sense for a feature that is disabled most of the time. > > Move the nohz_full storage to colder places. > > Signed-off-by: Frederic Weisbecker task_struct is still a bloody maze to me, but AFAICT there's *at least one* full non-optional cacheline - the signal handling faff - between cputime accounting and this new location, so: Reviewed-by: Valentin Schneider