On Tue, Apr 19, 2022 at 04:56:26PM -0700, Paul E. McKenney wrote: > On Tue, Apr 19, 2022 at 04:10:33PM -0400, Joel Fernandes wrote: > > On Tue, Apr 19, 2022 at 4:08 PM Joel Fernandes (Google) > > <joel@xxxxxxxxxxxxxxxxx> wrote: > > > > > > From: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> > > > > > > On systems with CONFIG_RCU_NOCB_CPU=y, 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= or rcu_nohz_full= kernel parameters provide a CPU list. > > > > > > Signed-off-by: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> > > > > Oops, forgot to add Reviewed-by tags: > > Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> > > Reviewed-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx> > > > > Paul, would you mind doing so, so I don't have to resend? Apologies. > > OK, but only because it passed an allmodconfig build this time. ;-) But the rcutorture TASKS03 scenario failed to build. Kernel test robot saw similar issues here: https://lore.kernel.org/all/202204201732.oTzYh0Xo-lkp@xxxxxxxxx/ Next version! ;-) Thanx, Paul > > Thanks, > > > > Joel > > > > > > > --- > > > 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/Documentation/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= boot parameter. > > > > > > + Note that this argument takes precedence over > > > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. > > > + > > > noiotrap [SH] Disables trapped I/O port accesses. > > > > > > 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. > > > > > > + 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= 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. > > > > > > +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 = false; > > > + bool offload_all = false; > > > struct rcu_data *rdp; > > > > > > +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) > > > + if (!rcu_state.nocb_is_setup) { > > > + need_rcu_nocb_mask = true; > > > + offload_all = 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 = true; > > > + offload_all = false; /* NO_HZ_FULL has its own mask. */ > > > + } > > > #endif /* #if defined(CONFIG_NO_HZ_FULL) */ > > > > > > 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) */ > > > > > > + if (offload_all) > > > + cpumask_setall(rcu_nocb_mask); > > > + > > > if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { > > > pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); > > > cpumask_and(rcu_nocb_mask, cpu_possible_mask, > > > -- > > > 2.36.0.rc0.470.gd361397f0d-goog > > >
