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Message-ID: <20110502161937.GC6524@linux.vnet.ibm.com> Date: Mon, 2 May 2011 09:19:37 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Josh Triplett <josh@...htriplett.org> Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com, patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org> Subject: Re: [PATCH tip/core/rcu 17/86] rcu: fix boost-tracing bug and update tracing documentation On Mon, May 02, 2011 at 09:18:24AM -0700, Paul E. McKenney wrote: > On Mon, May 02, 2011 at 01:33:01AM -0700, Paul E. McKenney wrote: > > 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. > > Here is the updated documentation update. And here is the bug fix. Thanx, Paul ------------------------------------------------------------------------ rcu: fix tracing bug thinko on boost-balk attribution The rcu_initiate_boost_trace() function mis-attributed refusals to initiate RCU priority boosting that were in fact due to its not yet being time to boost. This patch fixes the faulty comparison. Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 22a6a46..a21413d 100644 --- 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++; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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