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Tue, 25 Jul 2023 06:05:51 -0700 (PDT) X-Google-Smtp-Source: APBJJlF3IfiPQXJmTRIbnVDIkRhO1QGeOmJQGB2V7Ax+LFUYp7XQ/uOSm8c19TiPQx/PfreNkIV1Uw== X-Received: by 2002:a05:6000:4c3:b0:314:3f98:a788 with SMTP id h3-20020a05600004c300b003143f98a788mr9662062wri.7.1690290351507; Tue, 25 Jul 2023 06:05:51 -0700 (PDT) Received: from vschneid.remote.csb ([149.12.7.81]) by smtp.gmail.com with ESMTPSA id a15-20020adfeecf000000b00311d8c2561bsm16238717wrp.60.2023.07.25.06.05.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jul 2023 06:05:51 -0700 (PDT) From: Valentin Schneider To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, x86@kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org, Nicolas Saenz Julienne , Steven Rostedt , Masami Hiramatsu , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Peter Zijlstra , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Josh Poimboeuf , Jason Baron , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , Thomas =?utf-8?Q?Wei=C3=9Fschuh?= , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Yair Podemsky Subject: Re: [RFC PATCH v2 15/20] context-tracking: Introduce work deferral infrastructure In-Reply-To: References: <20230720163056.2564824-1-vschneid@redhat.com> <20230720163056.2564824-16-vschneid@redhat.com> Date: Tue, 25 Jul 2023 14:05:47 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Queue-Id: E17E3C0101 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: mn611doyj6kxeghc1cytpy8d3gepisrj X-HE-Tag: 1690290354-684226 X-HE-Meta: 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 Lk9AnAWW r3UXo+WhTfMuqQSC3yFD8+aDd1xjr5liIuI6GvJpjX5ZZggXrRVqgdUAwEYu6A+JnFvB//pAR11ctZut2cYz5CsSJc1Wz/HcQHe1HJ2/Sdh8sYIIdaGUxUc+3GxTEVWfp2yMUixVQEtVe+EIKN1no4dWmi5g0qe/GqQf9VWwwM75zIlM8Wox6pCJyD5d+LRInVDZnA3AbxCKI9H5CyrNvF4i6p7mgy5O+QSuOe8Mvf3MlpuZVG6lNf4+I18n6HP3isukpjWJi9Ag8RXNLTS0MsbQe09kMoCOtYUwU7gXnAwMNFdpJK9C6E6xSRGT85sGYmZ1LxJl0Py+lfcGsFrKclPi8QA== 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: On 25/07/23 13:22, Frederic Weisbecker wrote: > On Tue, Jul 25, 2023 at 11:10:31AM +0100, Valentin Schneider wrote: >> I have reasons! I just swept them under the rug and didn't mention them :D >> Also looking at the config dependencies again I got it wrong, but >> nevertheless that means I get to ramble about it. >> >> 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() >> >> Now, if we just make CONTEXT_TRACKING_WORK depend on CONTEXT_TRACKING_IDLE >> rather than CONTEXT_TRACKING_USER, we get to leverage the IPI deferral for >> NO_HZ_IDLE kernels - in other words, we get to keep idle CPUs idle longer. >> >> It's a completely different argument than reducing interference for >> NOHZ_FULL userspace applications and I should have at the very least >> mentioned it in the cover letter, but it's the exact same backing >> mechanism. >> >> Looking at it again, I'll probably make the CONTEXT_IDLE thing a separate >> patch with a proper changelog. > > Ok should that be a seperate Kconfig? This indeed can bring power improvement > but at the cost of more overhead from the sender. A balance to be measured... Yep agreed, I'll make that an optional config.