From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com,
fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com,
Alexander Gordeev <agordeev@redhat.com>
Subject: Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Date: Thu, 30 Jul 2015 08:25:17 -0700 [thread overview]
Message-ID: <20150730152517.GE27280@linux.vnet.ibm.com> (raw)
In-Reply-To: <20150730122835.GX19282@twins.programming.kicks-ass.net>
On Thu, Jul 30, 2015 at 02:28:35PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 17, 2015 at 03:30:53PM -0700, Paul E. McKenney wrote:
> > + if (n > rcu_capacity[MAX_RCU_LVLS])
> > + panic("rcu_init_geometry: rcu_capacity[] is too small");
>
> How can this ever happen? We _know_ NR_CPUS at compile time, there's no
> way we can get more CPUs than that -- even if the hardware has more,
> we'll stop enumerating.
You can make this happen by building with CONFIG_RCU_FANOUT=2 and
CONFIG_RCU_FANOUT_LEAF=2, then running on a system with more than 16 CPUs.
The kernel boot parameter rcutree.rcu_fanout_leaf=2 can be substituted for
CONFIG_RCU_FANOUT_LEAF=2, hence the need for a runtime test. I do this
sort of thing for my rcutorture testing in order to test a four-level
rcu_node tree with only 16 CPUs.
Thanx, Paul
next prev parent reply other threads:[~2015-07-30 15:25 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-17 22:30 [PATCH tip/core/rcu 0/12] Tree geometry-initialization simplifications for 4.3 Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 01/12] rcu: Provide more diagnostics for stalled GP kthread Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs Paul E. McKenney
2015-07-30 12:28 ` Peter Zijlstra
2015-07-30 15:25 ` Paul E. McKenney [this message]
2015-07-30 15:32 ` Peter Zijlstra
2015-07-30 15:34 ` Peter Zijlstra
2015-07-30 16:01 ` Paul E. McKenney
2015-07-30 15:54 ` Paul E. McKenney
2015-07-30 16:22 ` Peter Zijlstra
2015-07-31 15:53 ` Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 03/12] rcu: Remove superfluous local variable in rcu_init_geometry() Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 04/12] rcu: Cleanup rcu_init_geometry() code and arithmetics Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 05/12] rcu: Simplify rcu_init_geometry() capacity arithmetics Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 06/12] rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 07/12] rcu: Limit rcu_capacity[] size " Paul E. McKenney
2015-07-17 22:30 ` [PATCH tip/core/rcu 08/12] rcu: Remove unnecessary fields from rcu_state structure Paul E. McKenney
2015-07-17 22:31 ` [PATCH tip/core/rcu 09/12] rcu: Limit count of static data to the number of RCU levels Paul E. McKenney
2015-07-17 22:31 ` [PATCH tip/core/rcu 10/12] rcu: Simplify arithmetic to calculate number of RCU nodes Paul E. McKenney
2015-07-17 22:31 ` [PATCH tip/core/rcu 11/12] rcu: Shut up bogus gcc array bounds warning Paul E. McKenney
2015-07-17 22:31 ` [PATCH tip/core/rcu 12/12] rcu: Reset rcu_fanout_leaf if out of bounds Paul E. McKenney
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