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([2a0c:5a80:1d02:ba00:f4f8:7394:c8:7ddf]) by smtp.gmail.com with ESMTPSA id p3-20020a1c2903000000b003942a244ed7sm1947897wmp.28.2022.05.18.08.33.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 May 2022 08:33:03 -0700 (PDT) Message-ID: <6690c4c7119839a784d0d96523e832a10e04fcca.camel@redhat.com> Subject: Re: [PATCH 00/21] rcu/context-tracking: Merge RCU eqs-dynticks counter to context tracking v2 From: Nicolas Saenz Julienne To: Frederic Weisbecker , LKML Cc: Peter Zijlstra , Phil Auld , Alex Belits , Xiongfeng Wang , Neeraj Upadhyay , Thomas Gleixner , Yu Liao , Boqun Feng , "Paul E . McKenney" , Marcelo Tosatti , Paul Gortmaker , Uladzislau Rezki , Joel Fernandes Date: Wed, 18 May 2022 17:33:02 +0200 In-Reply-To: <20220503100051.2799723-1-frederic@kernel.org> References: <20220503100051.2799723-1-frederic@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.44.1 (3.44.1-1.fc36) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2022-05-03 at 12:00 +0200, Frederic Weisbecker wrote: > This mixes up the RCU dynticks counter and the context tracking state > updates into a single atomic instruction. This may serve several > purposes: >=20 > 1) Improve CPU isolation with deferring some disturbances until sensitive > userspace workload completes and goes to the kernel. This can take > several forms, for example smp_call_function_housekeeping() or > on_each_housekeeping_cpu() to enqueue and execute work on all > housekeeping CPUs. Then an atomic operation on ct->state can defer > the work on nohz_full CPUs until they run in kernel (or IPI them > if they are in kernel mode), see this proposal by Peter: > https://lore.kernel.org/all/20210929151723.162004989@infradead.org/#r >=20 > 2) Unearth sysidle (https://git.kernel.org/pub/scm/linux/kernel/git/paulm= ck/linux-rcu.git/commit/?h=3Dsysidle.2017.05.11a&id=3Dfe5ac724d81a3c7803e60= c2232718f212f3f38d4) > This feature allowed to shutdown the tick on the last housekeeping > CPU once the rest of the system is fully idle. We needed some proper > fully ordered context tracking for that. >=20 > Inspired by Peterz: https://lore.kernel.org/all/20210929151723.162004989@= infradead.org >=20 > Passed 100 hours of TREE01. >=20 > --- For the whole series: Reviewed-by: Nicolas Saenz Julienne Tested-by: Nicolas Saenz Julienne Thanks! --=20 Nicol=C3=A1s S=C3=A1enz