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Peter Anvin" , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Boris Ostrovsky , Josh Poimboeuf , Pawan Gupta , Sean Christopherson , Paolo Bonzini , Andy Lutomirski , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juri Lelli , Clark Williams , Yair Podemsky , Tomas Glozar , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Andrew Morton , Christoph Hellwig , Shuah Khan , Sami Tolvanen , Miguel Ojeda , Alice Ryhl , "Mike Rapoport (Microsoft)" , Samuel Holland , Rong Xu , Nicolas Saenz Julienne , Geert Uytterhoeven , Yosry Ahmed , "Kirill A. Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Subject: [PATCH v4 30/30] context-tracking: Add a Kconfig to enable IPI deferral for NO_HZ_IDLE Date: Tue, 14 Jan 2025 18:51:43 +0100 Message-ID: <20250114175143.81438-31-vschneid@redhat.com> In-Reply-To: <20250114175143.81438-1-vschneid@redhat.com> References: <20250114175143.81438-1-vschneid@redhat.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 With NO_HZ_IDLE, we get CONTEXT_TRACKING_IDLE, so we get these transitions: ct_idle_enter() ct_kernel_exit() ct_state_inc_clear_work() ct_idle_exit() ct_kernel_enter() ct_work_flush() With just CONTEXT_TRACKING_IDLE, ct_state_inc_clear_work() is just ct_state_inc() and ct_work_flush() is a no-op. However, making them be functional as if under CONTEXT_TRACKING_WORK would allow NO_HZ_IDLE to leverage IPI deferral to keep idle CPUs idle longer. Having this enabled for NO_HZ_IDLE is a different argument than for having it for NO_HZ_FULL (power savings vs latency/performance), but the backing mechanism is identical. Add a default-no option to enable IPI deferral with NO_HZ_IDLE. Signed-off-by: Valentin Schneider --- kernel/time/Kconfig | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index 7e8106a0d981f..c7398fe5382a0 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -183,9 +183,23 @@ config CONTEXT_TRACKING_USER_FORCE config CONTEXT_TRACKING_WORK bool - depends on HAVE_CONTEXT_TRACKING_WORK && CONTEXT_TRACKING_USER + depends on HAVE_CONTEXT_TRACKING_WORK && (CONTEXT_TRACKING_USER || CONTEXT_TRACKING_WORK_IDLE) default y +config CONTEXT_TRACKING_WORK_IDLE + bool + depends on HAVE_CONTEXT_TRACKING_WORK && CONTEXT_TRACKING_IDLE && !CONTEXT_TRACKING_USER + default n + help + This option enables deferral of some IPIs when they are targeted at CPUs + that are idle. This can help keep CPUs idle longer, but induces some + extra overhead to idle <-> kernel transitions and to IPI sending. + + Say Y if the power improvements are worth more to you than the added + overheads. + + Say N otherwise. + config NO_HZ bool "Old Idle dynticks config" help