On Fri, Sep 06, 2013 at 01:16:31PM -0400, Steven Rostedt wrote:
> On Fri, 6 Sep 2013 19:00:08 +0200
> Frederic Weisbecker <fweis...@gmail.com> wrote:
>
> > On Fri, Sep 06, 2013 at 12:52:38PM -0400, Steven Rostedt wrote:
> > > On Fri, 6 Sep 2013 18:40:18 +0200
> > > Frederic Weisbecker <fweis...@gmail.com> wrote:
> > >
> > > > > I can't use plain preempt_disable() in function tracing.
> > > > >
> > > > > Also, since it's a misnomer to say the cpu is idle in NO_HZ_FULL when
> > > > > we are coming from userspace, can we rename that?
> > > > >
> > > > > Perhaps we can also have a __rcu_is_cpu_tracking() (or whatever), with
> > > > > the "__" appended that does not do the preempt disable.
> > > >
> > > > rcu_is_cpu_eqs() is probably better. It refers to other related "eqs"
> > > > naming
> > > > in RCU APIs.
> > >
> > > But that will just confuse the heck out of people. When I see "eqs" I
> > > equate that with "equals". What does the rcu cpu equal?
> >
> > It's "extended quiescent state". There is already rcu_eqs_enter() and
> > rcu_eqs_exit().
> > You're right, may be we can rename that to avoid confusion with "equals". I
> > don't mind much.
> > I'm happy as long as the reader rcu_is_cpu_foo() and the writers
> > rcu_foo_enter() and
> > rcu_foo_exit() have consistant naming.
> >
>
> What exactly does "extended quiescent state" mean? (Note, that's a
> rhetorical question)
In which case my rhetorical (and therefore useless) answer has to be
"it is a quiescent state that is extended". ;-)
Sorry, couldn't resist...
> I wonder if we should change "rcu_cpu_ignore()" for "rcu_eqs_enter()"
> and "rcu_cpu_heed()" for "rcu_eqs_exit()", as IMHO that's much more
> straight forward to understand than trying to wrap you head around what
> a quiescent state is, and why we are entering it or exiting it.
>
> It also flat out explains to people that rcu is not processing that
> current CPU, and things like rcu_read_lock() should not be used.
>
> Then we can say "rcu_cpu_is_ignored()" for things like
> "rcu_is_cpu_eqs()".
Currently, none of RCU's _eqs functions are exported, so they have
the potential to confuse only people working on the RCU implementation
itself, who had better understand what "eqs" means.
But I do count your vote against "eqs" appearing in the name of any
function exported by RCU.
How about if I made rcu_is_cpu_idle() be as follows?
int rcu_is_cpu_idle(void)
{
int ret;
ret = (atomic_read(&per_cpu(rcu_dynticks.dynticks,
raw_smp_processor_id())) & 0x1) == 0;
return ret;
}
This should allow existing uses to function properly and should allow
you to use it as well.
Thanx, Paul
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