On Tue, Jan 26, 2021 at 01:36:23PM -0800, Yury Norov wrote:
> On Tue, Jan 26, 2021 at 9:12 AM Paul Gortmaker
> <[email protected]> wrote:
> >
> > With the core bitmap support now accepting "N" as a placeholder for
> > the end of the bitmap, "all" can be represented as "0-N" and has the
> > advantage of not being specific to RCU (or any other subsystem).
> >
> > So deprecate the use of "all" by removing documentation references
> > to it. The support itself needs to remain for now, since we don't
> > know how many people out there are using it currently, but since it
> > is in an __init area anyway, it isn't worth losing sleep over.
> >
> > Cc: Yury Norov <[email protected]>
> > Cc: Peter Zijlstra <[email protected]>
> > Cc: "Paul E. McKenney" <[email protected]>
> > Cc: Josh Triplett <[email protected]>
> > Signed-off-by: Paul Gortmaker <[email protected]>
> > ---
> > Documentation/admin-guide/kernel-parameters.txt | 4 +---
> > kernel/rcu/tree_plugin.h | 6 ++----
> > 2 files changed, 3 insertions(+), 7 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> > b/Documentation/admin-guide/kernel-parameters.txt
> > index a10b545c2070..a116c0ff0a91 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -4037,9 +4037,7 @@
> > see CONFIG_RAS_CEC help text.
> >
> > rcu_nocbs= [KNL]
> > - The argument is a cpu list, as described above,
> > - except that the string "all" can be used to
> > - specify every CPU on the system.
> > + The 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.
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > index 7e291ce0a1d6..56788dfde922 100644
> > --- a/kernel/rcu/tree_plugin.h
> > +++ b/kernel/rcu/tree_plugin.h
> > @@ -1463,14 +1463,12 @@ static void rcu_cleanup_after_idle(void)
> >
> > /*
> > * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
> > - * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
> > - * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
> > - * given, a warning is emitted and all CPUs are offloaded.
> > + * If the list is invalid, a warning is emitted and all CPUs are offloaded.
> > */
> > static int __init rcu_nocb_setup(char *str)
> > {
> > alloc_bootmem_cpumask_var(&rcu_nocb_mask);
> > - if (!strcasecmp(str, "all"))
> > + if (!strcasecmp(str, "all")) /* legacy: use "0-N"
> > instead */
>
> I think 'all' and 'none' is a good idea. It's simple and convenient.
> But if you don't
> like it, can you please at least put this comment in system log using
> WARN_ON_ONCE(). It's quite possible that Linux users don't read source code
> comments.
Please leave it silent. This has been available to RCU users for
quite some time, so suddenly spewing warnings at all of them is a bit
unfriendly. The extra code is negligible, and the documentation will
guide people more gently in the right direction. Plus I am the one who
would end up receiving complaints about the warnings, and I have much
better things to do with my time.
Thanx, Paul
> > cpumask_setall(rcu_nocb_mask);
> > else
> > if (cpulist_parse(str, rcu_nocb_mask)) {
> > --
> > 2.17.1
> >
