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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-04-14 19:33:59 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-04-14 19:33:59 -0700 |
| commit | 8d7dc9283f399e1fda4e48a1c453f689326d9396 (patch) | |
| tree | c63e3a78f675521d36c032319c26e9f85f942f20 | |
| parent | 590ee7dbd569a012df705a5204fc5f1066f52b8c (diff) | |
rcu: Control grace-period delays directly from value
In a misguided attempt to avoid an #ifdef, the use of the
gp_init_delay module parameter was conditioned on the corresponding
RCU_TORTURE_TEST_SLOW_INIT Kconfig variable, using IS_ENABLED() at
the point of use in the code. This meant that the compiler always saw
the delay, which meant that RCU_TORTURE_TEST_SLOW_INIT_DELAY had to be
unconditionally defined. This in turn caused "make oldconfig" to ask
pointless questions about the value of RCU_TORTURE_TEST_SLOW_INIT_DELAY
in cases where it was not even used.
This commit avoids these pointless questions by defining gp_init_delay
under #ifdef. In one branch, gp_init_delay is initialized to
RCU_TORTURE_TEST_SLOW_INIT_DELAY and is also a module parameter (thus
allowing boot-time modification), and in the other branch gp_init_delay
is a const variable initialized by default to zero.
This approach also simplifies the code at the delay point by eliminating
the IS_DEFINED(). Because gp_init_delay is constant zero in the no-delay
case intended for production use, the "gp_init_delay > 0" check causes
the delay to become dead code, as desired in this case. In addition,
this commit replaces magic constant "10" with the preprocessor variable
PER_RCU_NODE_PERIOD, which controls the number of grace periods that
are allowed to elapse at full speed before a delay is inserted.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:
Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| -rw-r--r-- | kernel/rcu/tree.c | 16 | ||||
| -rw-r--r-- | lib/Kconfig.debug | 1 |
2 files changed, 10 insertions, 7 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 233165da782f..8cf7304b2867 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -162,11 +162,14 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO; module_param(kthread_prio, int, 0644); -/* Delay in jiffies for grace-period initialization delays. */ -static int gp_init_delay = IS_ENABLED(CONFIG_RCU_TORTURE_TEST_SLOW_INIT) - ? CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY - : 0; +/* Delay in jiffies for grace-period initialization delays, debug only. */ +#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT +static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY; module_param(gp_init_delay, int, 0644); +#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */ +static const int gp_init_delay; +#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */ +#define PER_RCU_NODE_PERIOD 10 /* Number of grace periods between delays. */ /* * Track the rcutorture test sequence number and the update version @@ -1843,9 +1846,8 @@ static int rcu_gp_init(struct rcu_state *rsp) raw_spin_unlock_irq(&rnp->lock); cond_resched_rcu_qs(); ACCESS_ONCE(rsp->gp_activity) = jiffies; - if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_SLOW_INIT) && - gp_init_delay > 0 && - !(rsp->gpnum % (rcu_num_nodes * 10))) + if (gp_init_delay > 0 && + !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD))) schedule_timeout_uninterruptible(gp_init_delay); } diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 1ad74c0df01f..5f5ff7d7e5eb 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1268,6 +1268,7 @@ config RCU_TORTURE_TEST_SLOW_INIT_DELAY int "How much to slow down RCU grace-period initialization" range 0 5 default 3 + depends on RCU_TORTURE_TEST_SLOW_INIT help This option specifies the number of jiffies to wait between each rcu_node structure initialization. |