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Commit 20e9751b authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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[PATCH] rcu: simplify/improve batch tuning 



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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4b6c2cca

Documentation/kernel-parameters.txt

+0 −4
Original line number Diff line number Diff line
@@ -1357,10 +1357,6 @@ and is between 256 and 4096 characters. It is defined in the file 
	rcu.qlowmark=	[KNL,BOOT] Set threshold of queued

			RCU callbacks below which batch limiting is re-enabled.



	rcu.rsinterval=	[KNL,BOOT,SMP] Set the number of additional

			RCU callbacks to queued before forcing reschedule

			on all cpus.



	rdinit=		[KNL]

			Format: <full_path>

			Run specified binary instead of /init from the ramdisk,

include/linux/rcupdate.h

+2 −3
Original line number Diff line number Diff line
@@ -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);

kernel/rcupdate.c

+3 −8
Original line number Diff line number Diff line
@@ -71,9 +71,6 @@ static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; 
static int blimit = 10;

static int qhimark = 10000;

static int qlowmark = 100;

#ifdef CONFIG_SMP

static int rsinterval = 1000;

#endif



static atomic_t rcu_barrier_cpu_count;

static DEFINE_MUTEX(rcu_barrier_mutex);
@@ -86,8 +83,8 @@ static void force_quiescent_state(struct rcu_data *rdp, 
	int cpu;

	cpumask_t cpumask;

	set_need_resched();

	if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {

		rdp->last_rs_qlen = rdp->qlen;

	if (unlikely(!rcp->signaled)) {

		rcp->signaled = 1;

		/*

		 * Don't send IPI to itself. With irqs disabled,

		 * rdp->cpu is the current cpu.
@@ -301,6 +298,7 @@ static void rcu_start_batch(struct rcu_ctrlblk *rcp) 
		smp_mb();

		cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);



		rcp->signaled = 0;

	}

}
@@ -628,9 +626,6 @@ void synchronize_rcu(void) 
module_param(blimit, int, 0);

module_param(qhimark, int, 0);

module_param(qlowmark, int, 0);

#ifdef CONFIG_SMP

module_param(rsinterval, int, 0);

#endif

EXPORT_SYMBOL_GPL(rcu_batches_completed);

EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);

EXPORT_SYMBOL_GPL(call_rcu);