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From: Kent Overstreet To: Sebastian Andrzej Siewior Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Ben Segall , Daniel Bristot de Oliveira , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Klara Modin , Mel Gorman , Peter Zijlstra , Steven Rostedt , Suren Baghdasaryan , Thomas Gleixner , Valentin Schneider , Vincent Guittot Subject: Re: [PATCH] sched/task_struct: Move alloc_tag to the end of the struct. Message-ID: References: <20240621102750.oH9p1FQq@linutronix.de> <20240628094944.QwcHkf8J@linutronix.de> <20240628195553.G48MpeQ6@linutronix.de> <20240630211142.kZAs9f0p@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240630211142.kZAs9f0p@linutronix.de> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 8BDF51C0008 X-Stat-Signature: 71prfzstgoi1gq67qdgica4ieys3tj4w X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1719782624-105472 X-HE-Meta: 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 Kqdu4YUE sVvfUZ2DX5uKnif0pBPoGRSSEZAId+2rxh/WiRbUh/ZEvRy4GIY953EXQB7vRYgKQTDUHkSJa7G0sqmCB+Aj1Z4jZp09eGaamOLw1KA5YwS3YScRJLiwWyP/3SXdmJS/k5VH6fp4icmqxZ+ppGe04zNjLRhn39WfcyO4DdjPpPEDhbyM= 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 Sun, Jun 30, 2024 at 11:11:42PM GMT, Sebastian Andrzej Siewior wrote: > On 2024-06-28 16:20:27 [-0400], Kent Overstreet wrote: > > > Kent, you said you didn't want it where it currently is. Fine. You said > > > you want it at the front next to `flags'. This isn't going to work since > > > there is no space left. You didn't make another suggestion or say how to > > > make room. > > > > It doesn't need to be on the exact same cacheline, just as near as you > > can get it. > > the first possible thing would be somewhere after the scheduler. > However, what difference does it make if it s two cache lines later or > more? I don't understand the requirement "closer". take advantage of CPU prefetching; CPUs will bring in more than just the cacheline you touched because 64 bytes is small and it's cheap to fetch from the same DRAM bank while it's open.