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Message-Id: <20071217152943.10470215.dada1@cosmosbay.com>
Date: Mon, 17 Dec 2007 15:29:43 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: "parag.warudkar@...il.com" <parag.warudkar@...il.com>
Cc: linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: init_timer_deferrable conversion
On Mon, 17 Dec 2007 09:55:04 +0100
Eric Dumazet <dada1@...mosbay.com> wrote:
> On Sun, 16 Dec 2007 22:00:23 -0500 (EST)
> Parag Warudkar <parag.warudkar@...il.com> wrote:
>
> > In my quest to get the wake-ups from idle per second down to bare minimum,
> > I noticed 3 places in the kernel that could benefit from
> > using init_timer_deferrable() instead of init_timer() -
> >
> > a) drivers/net/sky2.c - watchdog_timer. This was showing up high on
> > Powertop's list of things that cause routine wakeups from idle. After
> > converting to init_timer_deferrable() the wakeups went down and this one
> > no longer shows up in powertop's list. 25% reduction.
> >
> > b) kernel/time/clocksource.c - watchdog_timer - same story as sky2.c
> >
> > c) net/core/neighbour.c - gc_timer - Most benefit from deferrable timer.
>
> neigh_periodic_timer() is actually doing almost nothing per round, since it
> looks only one slot of hash table. We could probably convert it to a
> workqueue and scan whole table at once.
>
Parag, could you please try this patch ?
[NET] ARP : Convert neigh garbage collection from softirq to workqueue
Current neigh_periodic_timer() function is fired by timer IRQ, and
scans one hash bucket out of a potentially big number.
As we are supposed to scan whole hash table in 15 seconds, this means
neigh_periodic_timer() can be fired very often. (depending on the number
of concurrent hash entries we stored in this table)
Converting this to a workqueue permits scaning whole table, minimizing icache
pollution, and firing this work every 15 seconds, independantly of hash table
size.
Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
include/net/neighbour.h | 4 -
net/core/neighbour.c | 89 ++++++++++++++++++--------------------
2 files changed, 45 insertions(+), 48 deletions(-)
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index a4f2618..fdb9251 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -24,6 +24,7 @@
#include <linux/err.h>
#include <linux/sysctl.h>
+#include <linux/workqueue.h>
#include <net/rtnetlink.h>
#define NUD_IN_TIMER (NUD_INCOMPLETE|NUD_REACHABLE|NUD_DELAY|NUD_PROBE)
@@ -155,7 +156,7 @@ struct neigh_table
int gc_thresh2;
int gc_thresh3;
unsigned long last_flush;
- struct timer_list gc_timer;
+ struct delayed_work gc_work;
struct timer_list proxy_timer;
struct sk_buff_head proxy_queue;
atomic_t entries;
@@ -166,7 +167,6 @@ struct neigh_table
struct neighbour **hash_buckets;
unsigned int hash_mask;
__u32 hash_rnd;
- unsigned int hash_chain_gc;
struct pneigh_entry **phash_buckets;
#ifdef CONFIG_PROC_FS
struct proc_dir_entry *pde;
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 4b6dd1e..495ab19 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -637,75 +637,74 @@ static void neigh_connect(struct neighbour *neigh)
hh->hh_output = neigh->ops->hh_output;
}
-static void neigh_periodic_timer(unsigned long arg)
+static void neigh_periodic_work(struct work_struct *work)
{
- struct neigh_table *tbl = (struct neigh_table *)arg;
+ struct neigh_table *tbl = container_of(work, struct neigh_table, gc_work.work);
struct neighbour *n, **np;
- unsigned long expire, now = jiffies;
+ unsigned int i;
NEIGH_CACHE_STAT_INC(tbl, periodic_gc_runs);
- write_lock(&tbl->lock);
+ write_lock_bh(&tbl->lock);
/*
* periodically recompute ReachableTime from random function
*/
- if (time_after(now, tbl->last_rand + 300 * HZ)) {
+ if (time_after(jiffies, tbl->last_rand + 300 * HZ)) {
struct neigh_parms *p;
- tbl->last_rand = now;
+ tbl->last_rand = jiffies;
for (p = &tbl->parms; p; p = p->next)
p->reachable_time =
neigh_rand_reach_time(p->base_reachable_time);
}
- np = &tbl->hash_buckets[tbl->hash_chain_gc];
- tbl->hash_chain_gc = ((tbl->hash_chain_gc + 1) & tbl->hash_mask);
+ for (i = 0 ; i <= tbl->hash_mask; i++) {
+ np = &tbl->hash_buckets[i];
- while ((n = *np) != NULL) {
- unsigned int state;
+ while ((n = *np) != NULL) {
+ unsigned int state;
- write_lock(&n->lock);
+ write_lock(&n->lock);
- state = n->nud_state;
- if (state & (NUD_PERMANENT | NUD_IN_TIMER)) {
- write_unlock(&n->lock);
- goto next_elt;
- }
+ state = n->nud_state;
+ if (state & (NUD_PERMANENT | NUD_IN_TIMER)) {
+ write_unlock(&n->lock);
+ goto next_elt;
+ }
- if (time_before(n->used, n->confirmed))
- n->used = n->confirmed;
+ if (time_before(n->used, n->confirmed))
+ n->used = n->confirmed;
- if (atomic_read(&n->refcnt) == 1 &&
- (state == NUD_FAILED ||
- time_after(now, n->used + n->parms->gc_staletime))) {
- *np = n->next;
- n->dead = 1;
+ if (atomic_read(&n->refcnt) == 1 &&
+ (state == NUD_FAILED ||
+ time_after(jiffies, n->used + n->parms->gc_staletime))) {
+ *np = n->next;
+ n->dead = 1;
+ write_unlock(&n->lock);
+ neigh_cleanup_and_release(n);
+ continue;
+ }
write_unlock(&n->lock);
- neigh_cleanup_and_release(n);
- continue;
- }
- write_unlock(&n->lock);
next_elt:
- np = &n->next;
+ np = &n->next;
+ }
+ /*
+ * It's fine to release lock here, even if hash table
+ * grows while we are preempted.
+ */
+ write_unlock_bh(&tbl->lock);
+ cond_resched();
+ write_lock_bh(&tbl->lock);
}
-
/* Cycle through all hash buckets every base_reachable_time/2 ticks.
* ARP entry timeouts range from 1/2 base_reachable_time to 3/2
* base_reachable_time.
*/
- expire = tbl->parms.base_reachable_time >> 1;
- expire /= (tbl->hash_mask + 1);
- if (!expire)
- expire = 1;
-
- if (expire>HZ)
- mod_timer(&tbl->gc_timer, round_jiffies(now + expire));
- else
- mod_timer(&tbl->gc_timer, now + expire);
-
- write_unlock(&tbl->lock);
+ schedule_delayed_work(&tbl->gc_work,
+ tbl->parms.base_reachable_time >> 1);
+ write_unlock_bh(&tbl->lock);
}
static __inline__ int neigh_max_probes(struct neighbour *n)
@@ -1370,10 +1369,8 @@ void neigh_table_init_no_netlink(struct neigh_table *tbl)
get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
rwlock_init(&tbl->lock);
- setup_timer(&tbl->gc_timer, neigh_periodic_timer, (unsigned long)tbl);
- tbl->gc_timer.expires = now + 1;
- add_timer(&tbl->gc_timer);
-
+ INIT_DELAYED_WORK_DEFERRABLE(&tbl->gc_work, neigh_periodic_work);
+ schedule_delayed_work(&tbl->gc_work, tbl->parms.reachable_time);
setup_timer(&tbl->proxy_timer, neigh_proxy_process, (unsigned long)tbl);
skb_queue_head_init_class(&tbl->proxy_queue,
&neigh_table_proxy_queue_class);
@@ -1408,7 +1405,8 @@ int neigh_table_clear(struct neigh_table *tbl)
struct neigh_table **tp;
/* It is not clean... Fix it to unload IPv6 module safely */
- del_timer_sync(&tbl->gc_timer);
+ cancel_delayed_work(&tbl->gc_work);
+ flush_scheduled_work();
del_timer_sync(&tbl->proxy_timer);
pneigh_queue_purge(&tbl->proxy_queue);
neigh_ifdown(tbl, NULL);
@@ -1678,7 +1676,6 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl,
.ndtc_last_rand = jiffies_to_msecs(rand_delta),
.ndtc_hash_rnd = tbl->hash_rnd,
.ndtc_hash_mask = tbl->hash_mask,
- .ndtc_hash_chain_gc = tbl->hash_chain_gc,
.ndtc_proxy_qlen = tbl->proxy_queue.qlen,
};
--
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