Re: [PATCH tip/core/rcu 17/86] rcu: fix boost-tracing bug and update tracing documentation

Paul E. McKenney
2011-05-02T08:33:13Z

On Sun, May 01, 2011 at 08:43:10AM -0700, Josh Triplett wrote:
> The bugfix here should really go in a separate commit from the updated
> documentation. Also:
>
> On Sun, May 01, 2011 at 06:20:57AM -0700, Paul E. McKenney wrote:
> > --- a/Documentation/RCU/trace.txt
> > +++ b/Documentation/RCU/trace.txt
> > @@ -10,34 +10,37 @@ for rcutree and next for rcutiny.
> >
> > CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
> >
> > -These implementations of RCU provides five debugfs files under the
> > +These implementations of RCU provides seven debugfs files under the
>
> s/seven/several/, so this doesn't continue to need updates as you add
> more tracing? It doesn't seem entirely accurate even now, given that
> the set of files available now depends on CONFIG_RCU_BOOST.

Good point, will fix.

> > top-level directory RCU: rcu/rcudata (which displays fields in struct
>
> RCU or rcu?

Indeed, "rcu". Will fix.

> > rcu_data), rcu/rcudata.csv (which is a .csv spreadsheet version of
> > rcu/rcudata), rcu/rcugp (which displays grace-period counters),
> > -rcu/rcuhier (which displays the struct rcu_node hierarchy), and
> > +rcu/rcuhier (which displays the struct rcu_node hierarchy),
> > rcu/rcu_pending (which displays counts of the reasons that the
> > -rcu_pending() function decided that there was core RCU work to do).
> > +rcu_pending() function decided that there was core RCU work to do),
> > +rcu/rcutorture (which displays rcutorture test progress), and, if the
> > +kernel is built with CONFIG_RCU_BOOST, rcu/rcuboost (which displays RCU
> > +boosting statistics).
>
> I think this would work better as a list:
>
> rcu/rcudata:
> Displays fields in struct rcu_data.
> rcu/rcudata.csv:
> Comma-separated values spreadsheet version of rcudata.
> rcu/rcugp:
> Displays grace-period counters.
> rcu/rcuhier
> Displays the struct rcu_node hierarchy.
> rcu/rcu_pending:
> Displays counts of the reasons rcu_pending() decided that RCU had
> work to do.
> rcu/rcutorture:
> Displays rcutorture test progress.
> rcu/rcuboost
> Displays RCU boosting statistics. Only present if
> CONFIG_RCU_BOOST=y.
>
> Feel free to put the descriptions on the same lines as the filenames if
> you prefer; however, I thought this style worked better for the
> descriptions longer than one line.

Makes sense, will do a list.

> Also, does rcu/rcutorture appear with rcutorture not loaded? Hopefully
> not, since rcutorture shouldn't take up any additional resources when
> not loaded.

Not much choice, unfortunately. If I put the info into rcutorture, then
I lose it when rcutorture is unloaded. This is problematic in automated
tests that repeatedly load and unload rcutorture.

But the amount of data is small, and I set things up so that TINY_RCU
can omit this. TREE_RCU is big enough that it doesn't really matter.

> > --- a/kernel/rcutree_plugin.h
> > +++ b/kernel/rcutree_plugin.h
> > @@ -1086,7 +1086,7 @@ static void rcu_initiate_boost_trace(struct rcu_node *rnp)
> > else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
> > rnp->n_balk_notblocked++;
> > else if (rnp->gp_tasks != NULL &&
> > - ULONG_CMP_GE(jiffies, rnp->boost_time))
> > + ULONG_CMP_LT(jiffies, rnp->boost_time))
> > rnp->n_balk_notyet++;
> > else
> > rnp->n_balk_nos++;
>
> This bugfix should go in a separate commit.

Excellent point, will fix.

Thanx, Paul