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[PATCH] rcu: simplify/improve batch tuning

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Kill a hard-to-calculate 'rsinterval' boot parameter and per-cpu
rcu_data.last_rs_qlen.  Instead, it adds adds a flag rcu_ctrlblk.signaled,
which records the fact that one of CPUs has sent a resched IPI since the
last rcu_start_batch().

Roughly speaking, we need two rcu_start_batch()s in order to move callbacks
from ->nxtlist to ->donelist.  This means that when ->qlen exceeds qhimark
and continues to grow, we should send a resched IPI, and then do it again
after we gone through a quiescent state.

On the other hand, if it was already sent, we don't need to do it again
when another CPU detects overflow of the queue.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-10-04 02:17:17 -07:00 • committed by Linus Torvalds
parent 4b6c2cca6e
commit 20e9751bd9
3 changed files with 5 additions and 15 deletions
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5
include/linux/rcupdate.h
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@ -66,6 +66,8 @@ struct rcu_ctrlblk {
long completed; /* Number of the last completed batch */
int next_pending; /* Is the next batch already waiting? */
int signaled;
spinlock_t lock ____cacheline_internodealigned_in_smp;
cpumask_t cpumask; /* CPUs that need to switch in order */
/* for current batch to proceed. */
@ -106,9 +108,6 @@ struct rcu_data {
long blimit; /* Upper limit on a processed batch */
int cpu;
struct rcu_head barrier;
#ifdef CONFIG_SMP
long last_rs_qlen; /* qlen during the last resched */
#endif
};
DECLARE_PER_CPU(struct rcu_data, rcu_data);