From 20e9751bd9dd6b832fd84ada27840360f7e877f1 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Wed, 4 Oct 2006 02:17:17 -0700
Subject: [PATCH] [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: 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>
---
Documentation/kernel-parameters.txt | 4 ----
include/linux/rcupdate.h | 5 ++---
kernel/rcupdate.c | 11 +++--------
3 files changed, 5 insertions(+), 15 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 12b3b24bfd2f..e1543a32a557 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -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,
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b4ca73d65891..f6dd71bf8a4b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -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);
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 523e46483b99..26bb5ffe1ef1 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -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);
--
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