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    SubjectRe: [PATCH 5/6] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter
    On Wed, Nov 17, 2021 at 04:56:36PM +0100, Frederic Weisbecker wrote:
    > 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>
    > ---
    > kernel/rcu/tree_nocb.h | 10 ++++++----

    Could you please also update kernel-parameters.txt?

    > 1 file changed, 6 insertions(+), 4 deletions(-)
    >
    > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
    > index 1871f15b8472..3845f1885ffc 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);
    > + }

    Wouldn't "*str == '='" indicate that the parameter passed in was of
    the form "rcu_nocbs==8"?

    Or am I misreading the next_arg() function in lib/cmdline.c?

    If I am reading it correctly, doesn't the test instead want to be
    something of the form "if (str && *str)"?

    Thanx, Paul

    > }
    > 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
    >

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