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[213.44.135.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce57d3b9sm24483884f8f.11.2025.10.14.08.26.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Oct 2025 08:26:05 -0700 (PDT) From: Valentin Schneider To: Juri Lelli Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnaldo Carvalho de Melo , Josh Poimboeuf , Paolo Bonzini , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Sami Tolvanen , "David S. Miller" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Mel Gorman , Andrew Morton , Masahiro Yamada , Han Shen , Rik van Riel , Jann Horn , Dan Carpenter , Oleg Nesterov , Clark Williams , Yair Podemsky , Marcelo Tosatti , Daniel Wagner , Petr Tesarik Subject: Re: [PATCH v6 00/29] context_tracking,x86: Defer some IPIs until a user->kernel transition In-Reply-To: References: <20251010153839.151763-1-vschneid@redhat.com> Date: Tue, 14 Oct 2025 17:26:04 +0200 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 5Peky1Kq56IpjqzJR5noPZGcc4DHUZEQ2zs3YBqbAtc_1760455567 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 360B14000D X-Stat-Signature: gd3etexo6xij83ueq8iiuonc1mtcp6bi X-Rspam-User: X-HE-Tag: 1760455572-766588 X-HE-Meta: U2FsdGVkX1/KvvMfWQe6wzMTPKZ7JtLA3b5joG80dvJz2wSAn4aBY88bYaIKBXhfFRaLcYlE3XV7WqBeiOyLpheUu3XIunhuddK4JEiGKInWRnxpOoV+/M6ZoOE2i2ndNYCMzpewzWg9sanv4njmu0dbxZN0Y5BV9OohlQE/Sq29Qjbv5sYUTyv4RT5VrrG1zithRjeGB2Myf0hxjoCqhiln/YStUQAu3M5srDzmbm/z47BO+/vKOPrVXCNcLkJjdVhLfPS7SCRQegu0GDB4m1kACCCxC+YBlUVS9rKkjcuTFE3CP0HdpUYalt1pgthvvmetlnbx+ZguG26n51k3v+y45SFMe9W5zY9y49a3s9M0Qc8T8sSRkap+G6o7AtHKfiFDungbYq4k3DaP8qEdIiRqO8lzPZK9Z38nIATUODAclSeKHdUB/xWgUQApA7BPPTa43esjnXahgS6b30vs30JLTP/Ca2OkUHqdb/Ynm9xlWbWeEkHhsOZylSOjGhHBmW0zEYIm+TKWvg2OVpZ0CePevFIxeFgSTavSiYgpRC9dJ2WOnRNwrn+dupHLVn9KEm+pMR7GYaFSjSPWmVIDgZ/XTlcaoaQnVEow5fRXT5Gbw5HpeBrs4LiyphHZbMQqY9ZJ268+zPFYqzxF8Z3VVnmcz40zb2euAvHabzvBSdOMAY4OU9+UQ9hlch9/vjcG1ChnRN51DnL555DGHyDu1JFHn0FmR+Pz6Vung7U1RUDcGh4c91eQAOgRQusL0itHp+gGR0Ly51lUiRur6PaORDyBZqFw83srOPK8oSsBGka3kIYoqd8tAAoU02VAqe/H4x269cV7C+anFg1/y8xk50Y0tBhRa1RK2n1lYUgMfQ5RWUPG3faaerFDiPqVjpu8dTMRaibK2s6oklZpom6U12w00d4YKNZ50HPbDvmyAt6NY9EHaHh1bkAyzziZqKCx+RyVinCpJJFPHQUa/kS vL2NJPe4 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 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 14/10/25 14:58, Juri Lelli wrote: >> Noise >> +++++ >> >> Xeon E5-2699 system with SMToff, NOHZ_FULL, isolated CPUs. >> RHEL10 userspace. >> >> Workload is using rteval (kernel compilation + hackbench) on housekeeping CPUs >> and a dummy stay-in-userspace loop on the isolated CPUs. The main invocation is: >> >> $ trace-cmd record -e "ipi_send_cpumask" -f "cpumask & CPUS{$ISOL_CPUS}" \ >> -e "ipi_send_cpu" -f "cpu & CPUS{$ISOL_CPUS}" \ >> rteval --onlyload --loads-cpulist=$HK_CPUS \ >> --hackbench-runlowmem=True --duration=$DURATION >> >> This only records IPIs sent to isolated CPUs, so any event there is interference >> (with a bit of fuzz at the start/end of the workload when spawning the >> processes). All tests were done with a duration of 6 hours. >> >> v6.17 >> o ~5400 IPIs received, so about ~200 interfering IPI per isolated CPU >> o About one interfering IPI just shy of every 2 minutes >> >> v6.17 + patches >> o Zilch! > > Nice. :) > > About performance, can we assume housekeeping CPUs are not affected by > the change (they don't seem to use the trick anyway) or do we want/need > to collect some numbers on them as well just in case (maybe more > throughput oriented)? > So for the text_poke IPI yes, because this is all done through context_tracking which doesn't imply housekeeping CPUs. For the TLB flush faff the HK CPUs get two extra writes per kernel entry cycle (one at entry and one at exit, for that stupid signal) which I expect to be noticeable but small-ish. I can definitely go and measure that. > Thanks, > Juri