lkml.org 
[lkml]   [2021]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5/6] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter
    Date
    If a user wants to boot without any CPU in offloaded mode initially but
    with the possibility to offload them later using cpusets, provide a way
    to simply pass an empty "rcu_nocbs" kernel parameter which will enforce
    the creation of dormant nocb kthreads.

    Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
    Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
    Cc: Boqun Feng <boqun.feng@gmail.com>
    Cc: Uladzislau Rezki <urezki@gmail.com>
    Cc: Josh Triplett <josh@joshtriplett.org>
    Cc: Joel Fernandes <joel@joelfernandes.org>
    ---
    .../admin-guide/kernel-parameters.txt | 26 ++++++++++++-------
    kernel/rcu/tree_nocb.h | 10 ++++---
    2 files changed, 23 insertions(+), 13 deletions(-)

    diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
    index cd860dc7c60b..6ff1a5f06383 100644
    --- a/Documentation/admin-guide/kernel-parameters.txt
    +++ b/Documentation/admin-guide/kernel-parameters.txt
    @@ -4351,20 +4351,28 @@
    Disable the Correctable Errors Collector,
    see CONFIG_RAS_CEC help text.

    - rcu_nocbs= [KNL]
    - The argument is a cpu list, as described above.
    + rcu_nocbs[=cpu-list]
    + [KNL] The optional argument is a cpu list,
    + as described above.

    - In kernels built with CONFIG_RCU_NOCB_CPU=y, set
    - the specified list of CPUs to be no-callback CPUs.
    - Invocation of these CPUs' RCU callbacks will be
    - offloaded to "rcuox/N" kthreads created for that
    - purpose, where "x" is "p" for RCU-preempt, and
    - "s" for RCU-sched, and "N" is the CPU number.
    - This reduces OS jitter on the offloaded CPUs,
    + In kernels built with CONFIG_RCU_NOCB_CPU=y, enable the
    + no-callback CPU mode. Invocation of such CPUs' RCU
    + callbacks will be offloaded to "rcuox/N" kthreads
    + created for that purpose, where "x" is "p" for
    + RCU-preempt, and "s" for RCU-sched, and "N" is the CPU
    + number. This reduces OS jitter on the offloaded CPUs,
    which can be useful for HPC and real-time
    workloads. It can also improve energy efficiency
    for asymmetric multiprocessors.

    + If a cpulist is passed as an argument, the specified
    + list of CPUs is set to no-callback mode from boot.
    +
    + If otherwise the '=' sign and the cpulist arguments are
    + omitted, no CPU will be set to no-callback mode from
    + boot but cpuset will allow for toggling that mode at
    + runtime.
    +
    rcu_nocb_poll [KNL]
    Rather than requiring that offloaded CPUs
    (specified by rcu_nocbs= above) explicitly
    diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
    index 9d37916278d4..d915780d40c8 100644
    --- a/kernel/rcu/tree_nocb.h
    +++ b/kernel/rcu/tree_nocb.h
    @@ -66,14 +66,16 @@ static bool rcu_nocb_is_setup;
    static int __init rcu_nocb_setup(char *str)
    {
    alloc_bootmem_cpumask_var(&rcu_nocb_mask);
    - if (cpulist_parse(str, rcu_nocb_mask)) {
    - pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
    - cpumask_setall(rcu_nocb_mask);
    + if (*str == '=') {
    + if (cpulist_parse(++str, rcu_nocb_mask)) {
    + pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
    + cpumask_setall(rcu_nocb_mask);
    + }
    }
    rcu_nocb_is_setup = true;
    return 1;
    }
    -__setup("rcu_nocbs=", rcu_nocb_setup);
    +__setup("rcu_nocbs", rcu_nocb_setup);

    static int __init parse_rcu_nocb_poll(char *arg)
    {
    --
    2.25.1
    \
     
     \ /
      Last update: 2021-11-23 01:38    [W:4.118 / U:0.252 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site