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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-12-15 01:36:02 (GMT) |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-12-17 20:34:49 (GMT) |
commit | b52573d2796274f7f31cfeff7185c320adcd4f12 (patch) | |
tree | 61580632fa8fbf80225ba7339274ada0c013a01b /kernel | |
parent | 0209f6490b030f35349a2bb71294f3fd75b0f36d (diff) | |
download | linux-fsl-qoriq-b52573d2796274f7f31cfeff7185c320adcd4f12.tar.xz |
rcu: reduce __call_rcu()-induced contention on rcu_node structures
When the current __call_rcu() function was written, the expedited
APIs did not exist. The __call_rcu() implementation therefore went
to great lengths to detect the end of old grace periods and to start
new ones, all in the name of reducing grace-period latency. Now the
expedited APIs do exist, and the usage of __call_rcu() has increased
considerably. This commit therefore causes __call_rcu() to avoid
worrying about grace periods unless there are a large number of
RCU callbacks stacked up on the current CPU.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/rcutree.c | 38 |
1 files changed, 21 insertions, 17 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 01c8ad3..d0ddfea 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1435,22 +1435,11 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), */ local_irq_save(flags); rdp = this_cpu_ptr(rsp->rda); - rcu_process_gp_end(rsp, rdp); - check_for_new_grace_period(rsp, rdp); /* Add the callback to our list. */ *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; - /* Start a new grace period if one not already started. */ - if (!rcu_gp_in_progress(rsp)) { - unsigned long nestflag; - struct rcu_node *rnp_root = rcu_get_root(rsp); - - raw_spin_lock_irqsave(&rnp_root->lock, nestflag); - rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */ - } - /* * Force the grace period if too many callbacks or too long waiting. * Enforce hysteresis, and don't invoke force_quiescent_state() @@ -1459,12 +1448,27 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * is the only one waiting for a grace period to complete. */ if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) { - rdp->blimit = LONG_MAX; - if (rsp->n_force_qs == rdp->n_force_qs_snap && - *rdp->nxttail[RCU_DONE_TAIL] != head) - force_quiescent_state(rsp, 0); - rdp->n_force_qs_snap = rsp->n_force_qs; - rdp->qlen_last_fqs_check = rdp->qlen; + + /* Are we ignoring a completed grace period? */ + rcu_process_gp_end(rsp, rdp); + check_for_new_grace_period(rsp, rdp); + + /* Start a new grace period if one not already started. */ + if (!rcu_gp_in_progress(rsp)) { + unsigned long nestflag; + struct rcu_node *rnp_root = rcu_get_root(rsp); + + raw_spin_lock_irqsave(&rnp_root->lock, nestflag); + rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */ + } else { + /* Give the grace period a kick. */ + rdp->blimit = LONG_MAX; + if (rsp->n_force_qs == rdp->n_force_qs_snap && + *rdp->nxttail[RCU_DONE_TAIL] != head) + force_quiescent_state(rsp, 0); + rdp->n_force_qs_snap = rsp->n_force_qs; + rdp->qlen_last_fqs_check = rdp->qlen; + } } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) force_quiescent_state(rsp, 1); local_irq_restore(flags); |