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[213.44.135.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce57ccb1sm28976327f8f.8.2025.10.15.06.16.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Oct 2025 06:16:15 -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: Wed, 15 Oct 2025 15:16:13 +0200 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: _o4YPkxIcRd-Pq6ZBnPfUyMmy1y4dEhL5Hpi2v-yz8Q_1760534177 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8701FA000A X-Stat-Signature: sfjgkbf3zz3jeknquir3xdk4a31sknrj X-HE-Tag: 1760534181-876848 X-HE-Meta: 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 dRs9Y5nM JifanhxMeg0610O6o67wf28N1jj6DfobV+SsgKkVpgnpvAYETltX0Z6QKFiVFDVkWORq+eqDnogeksAZiD52IqLkKf9MrPd7O4dECSL6h4N4FLcweDO1WO7sNbR7sHfSYlNRBcfhsl9a5zYueqMEVsmZjPGkVBTplQQsXtrLnwzB9F5a69bwvfcHuIJnlFzpmf2cvWbG4M2EY13cEQkOuNyu+6J+G3cMT9xlhv6zUmWcr92YaGa/zShAkeIV8WTdT2EplRx2s+1CpxTuv7UNfNbbIgizNN/L4XUL8DIpV1p1D5TYzu1cplcNpSjKeeKDpET0uvMG8JXUJr5NZx8l8SyrsM6ZIqkJIL+FuX7tnMjgOX5CcuLYcgAKGG4uXrwVGZYdCHtGzGdJelVe2tXjAr3nJ3vcpgjl6ybpfygCrA3wxY+DpOGPCpJ9a8evst3m39zsDWlsV+7Zqe44UNb4TMg/AsRpDN4XTwh0IGDjIDurPEDiKQzTwkwHIXVUNW8rqE4eme0BALAWhhlf8jJk+in53hLjGLATxEthyHLdU8xZ8b/imqiflW7BNUpcbyEJvWwnD3RuAeVUr42dWBml0MBlNjRTuN8wtUERV7vhNKOlcDEk= 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 17:26, Valentin Schneider wrote: > 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 housekeepi= ng CPUs >>> and a dummy stay-in-userspace loop on the isolated CPUs. The main invoc= ation 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=3D$HK_CPUS \ >>> --hackbench-runlowmem=3DTrue --duration=3D$DURATION >>> >>> This only records IPIs sent to isolated CPUs, so any event there is int= erference >>> (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 expe= ct > to be noticeable but small-ish. I can definitely go and measure that. > On that same Xeon E5-2699 system with the same tuning, the average time taken for 300M gettid syscalls on housekeeping CPUs is v6.17: 698.64ns =C2=B1 2.35ns v6.17 + series: 702.60ns =C2=B1 3.43ns So noticeable (~.6% worse) but not horrible? >> Thanks, >> Juri