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[34.150.221.228]) by smtp.gmail.com with ESMTPSA id y18-20020ac85f52000000b002ed08a7dc8dsm582804qta.13.2022.04.19.13.08.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Apr 2022 13:08:30 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: Joel Fernandes , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , "Paul E. McKenney" , rcu@vger.kernel.org, Steven Rostedt , rushikesh.s.kadam@intel.com, vineethrp@gmail.com, urezki@gmail.com Subject: [PATCH v4 rcu/dev] rcu/nocb: Add an option to offload all CPUs on boot Date: Tue, 19 Apr 2022 20:08:23 +0000 Message-Id: <20220419200823.2790490-1-joel@joelfernandes.org> X-Mailer: git-send-email 2.36.0.rc0.470.gd361397f0d-goog MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Joel Fernandes On systems with CONFIG_RCU_NOCB_CPU=3Dy, there is no default mask provided which ends up not offloading any CPU. This patch removes a dependency from the bootloader having to know about RCU and about how to provide the mask. With the new option enabled, all CPUs will be offloaded on boot unless rcu_nocbs=3D or rcu_nohz_full=3D kernel parameters provide a CPU list. Signed-off-by: Joel Fernandes Reviewed-by: Kalesh Singh Reviewed-by: Uladzislau Rezki (Sony) --- v4: Rebased on rcu/dev, fixed conflict with Frederick's patch changing location of nocb_is_setup variable. Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ kernel/rcu/Kconfig | 13 +++++++++++++ kernel/rcu/tree_nocb.h | 13 +++++++++++++ 3 files changed, 32 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 789ef586009b..1e82ecb7a649 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3572,6 +3572,9 @@ just as if they had also been called out in the rcu_nocbs=3D boot parameter. =20 + Note that this argument takes precedence over + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. + noiotrap [SH] Disables trapped I/O port accesses. =20 noirqdebug [X86-32] Disables the code which attempts to detect and @@ -4475,6 +4478,9 @@ no-callback mode from boot but the mode may be toggled at runtime via cpusets. =20 + Note that this argument takes precedence over + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. + rcu_nocb_poll [KNL] Rather than requiring that offloaded CPUs (specified by rcu_nocbs=3D above) explicitly diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index 1c630e573548..27aab870ae4c 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -262,6 +262,19 @@ config RCU_NOCB_CPU Say Y here if you need reduced OS jitter, despite added overhead. Say N here if you are unsure. =20 +config RCU_NOCB_CPU_DEFAULT_ALL + bool "Offload RCU callback processing from all CPUs by default" + depends on RCU_NOCB_CPU + default n + help + Use this option to offload callback processing from all CPUs + by default, in the absence of the rcu_nocbs or nohz_full boot + parameter. This also avoids the need to use any boot parameters + to achieve the effect of offloading all CPUs on boot. + + Say Y here if you want offload all CPUs by default on boot. + Say N here if you are unsure. + config TASKS_TRACE_RCU_READ_MB bool "Tasks Trace RCU readers use memory barriers in user and idle" depends on RCU_EXPERT && TASKS_TRACE_RCU diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 4cf9a29bba79..9f29f25a0cbc 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1197,11 +1197,21 @@ void __init rcu_init_nohz(void) { int cpu; bool need_rcu_nocb_mask =3D false; + bool offload_all =3D false; struct rcu_data *rdp; =20 +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) + if (!rcu_state.nocb_is_setup) { + need_rcu_nocb_mask =3D true; + offload_all =3D true; + } +#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */ + #if defined(CONFIG_NO_HZ_FULL) if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) need_rcu_nocb_mask =3D true; + offload_all =3D false; /* NO_HZ_FULL has its own mask. */ + } #endif /* #if defined(CONFIG_NO_HZ_FULL) */ =20 if (need_rcu_nocb_mask) { @@ -1222,6 +1232,9 @@ void __init rcu_init_nohz(void) cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); #endif /* #if defined(CONFIG_NO_HZ_FULL) */ =20 + if (offload_all) + cpumask_setall(rcu_nocb_mask); + if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { pr_info("\tNote: kernel parameter 'rcu_nocbs=3D', 'nohz_full', or 'isolc= pus=3D' contains nonexistent CPUs.\n"); cpumask_and(rcu_nocb_mask, cpu_possible_mask, --=20 2.36.0.rc0.470.gd361397f0d-goog