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ipvs: convert wrr scheduler to rcu

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The schedule method now needs _rcu list-traversal
primitive for svc->destinations. As the weight for some
dest can be reduced during dest selection, change the
algorithm to check weights by using minimum weights in the
1 .. max_weight-(di-1) range, with the same step (di). By this
way we ensure that there will be always a weight >= 1 check
before claiming that all destinations are overloaded.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
This commit is contained in:
Julian Anastasov 2013-03-22 11:46:48 +02:00 committed by Pablo Neira Ayuso
parent b310faad3e
commit 08cb2d032f
1 changed files with 103 additions and 64 deletions
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167
net/netfilter/ipvs/ip_vs_wrr.c
View File

@ -29,14 +29,45 @@
#include <net/ip_vs.h>
/* The WRR algorithm depends on some caclulations:
* - mw: maximum weight
* - di: weight step, greatest common divisor from all weights
* - cw: current required weight
* As result, all weights are in the [di..mw] range with a step=di.
*
* First, we start with cw = mw and select dests with weight >= cw.
* Then cw is reduced with di and all dests are checked again.
* Last pass should be with cw = di. We have mw/di passes in total:
*
* pass 1: cw = max weight
* pass 2: cw = max weight - di
* pass 3: cw = max weight - 2 * di
* ...
* last pass: cw = di
*
* Weights are supposed to be >= di but we run in parallel with
* weight changes, it is possible some dest weight to be reduced
* below di, bad if it is the only available dest.
*
* So, we modify how mw is calculated, now it is reduced with (di - 1),
* so that last cw is 1 to catch such dests with weight below di:
* pass 1: cw = max weight - (di - 1)
* pass 2: cw = max weight - di - (di - 1)
* pass 3: cw = max weight - 2 * di - (di - 1)
* ...
* last pass: cw = 1
*
*/
/*
* current destination pointer for weighted round-robin scheduling
*/
struct ip_vs_wrr_mark {
struct list_head *cl; /* current list head */
struct ip_vs_dest *cl; /* current dest or head */
int cw; /* current weight */
int mw; /* maximum weight */
int di; /* decreasing interval */
struct rcu_head rcu_head;
};
@ -88,10 +119,10 @@ static int ip_vs_wrr_init_svc(struct ip_vs_service *svc)
if (mark == NULL)
return -ENOMEM;
mark->cl = &svc->destinations;
mark->cw = 0;
mark->mw = ip_vs_wrr_max_weight(svc);
mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
mark->di = ip_vs_wrr_gcd_weight(svc);
mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
mark->cw = mark->mw;
svc->sched_data = mark;
return 0;
@ -100,24 +131,31 @@ static int ip_vs_wrr_init_svc(struct ip_vs_service *svc)
static int ip_vs_wrr_done_svc(struct ip_vs_service *svc)
{
struct ip_vs_wrr_mark *mark = svc->sched_data;
/*
* Release the mark variable
*/
kfree(svc->sched_data);
kfree_rcu(mark, rcu_head);
return 0;
}
static int ip_vs_wrr_update_svc(struct ip_vs_service *svc)
static int ip_vs_wrr_dest_changed(struct ip_vs_service *svc,
struct ip_vs_dest *dest)
{
struct ip_vs_wrr_mark *mark = svc->sched_data;
mark->cl = &svc->destinations;
mark->mw = ip_vs_wrr_max_weight(svc);
write_lock_bh(&svc->sched_lock);
mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
mark->di = ip_vs_wrr_gcd_weight(svc);
if (mark->cw > mark->mw)
mark->cw = 0;
mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
if (mark->cw > mark->mw || !mark->cw)
mark->cw = mark->mw;
else if (mark->di > 1)
mark->cw = (mark->cw / mark->di) * mark->di + 1;
write_unlock_bh(&svc->sched_lock);
return 0;
}
@ -128,80 +166,79 @@ static int ip_vs_wrr_update_svc(struct ip_vs_service *svc)
static struct ip_vs_dest *
ip_vs_wrr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
struct ip_vs_dest *dest;
struct ip_vs_dest *dest, *last, *stop = NULL;
struct ip_vs_wrr_mark *mark = svc->sched_data;
struct list_head *p;
bool last_pass = false, restarted = false;
IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
/*
* This loop will always terminate, because mark->cw in (0, max_weight]
* and at least one server has its weight equal to max_weight.
*/
write_lock(&svc->sched_lock);
p = mark->cl;
dest = mark->cl;
/* No available dests? */
if (mark->mw == 0)
goto err_noavail;
last = dest;
/* Stop only after all dests were checked for weight >= 1 (last pass) */
while (1) {
if (mark->cl == &svc->destinations) {
/* it is at the head of the destination list */
if (mark->cl == mark->cl->next) {
/* no dest entry */
ip_vs_scheduler_err(svc,
"no destination available: "
"no destinations present");
dest = NULL;
goto out;
}
mark->cl = svc->destinations.next;
mark->cw -= mark->di;
if (mark->cw <= 0) {
mark->cw = mark->mw;
/*
* Still zero, which means no available servers.
*/
if (mark->cw == 0) {
mark->cl = &svc->destinations;
ip_vs_scheduler_err(svc,
"no destination available");
dest = NULL;
goto out;
}
}
} else
mark->cl = mark->cl->next;
if (mark->cl != &svc->destinations) {
/* not at the head of the list */
dest = list_entry(mark->cl, struct ip_vs_dest, n_list);
list_for_each_entry_continue_rcu(dest,
&svc->destinations,
n_list) {
if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
atomic_read(&dest->weight) >= mark->cw) {
/* got it */
break;
}
atomic_read(&dest->weight) >= mark->cw)
goto found;
if (dest == stop)
goto err_over;
}
if (mark->cl == p && mark->cw == mark->di) {
/* back to the start, and no dest is found.
It is only possible when all dests are OVERLOADED */
dest = NULL;
ip_vs_scheduler_err(svc,
"no destination available: "
"all destinations are overloaded");
goto out;
mark->cw -= mark->di;
if (mark->cw <= 0) {
mark->cw = mark->mw;
/* Stop if we tried last pass from first dest:
* 1. last_pass: we started checks when cw > di but
* then all dests were checked for w >= 1
* 2. last was head: the first and only traversal
* was for weight >= 1, for all dests.
*/
if (last_pass ||
&last->n_list == &svc->destinations)
goto err_over;
restarted = true;
}
last_pass = mark->cw <= mark->di;
if (last_pass && restarted &&
&last->n_list != &svc->destinations) {
/* First traversal was for w >= 1 but only
* for dests after 'last', now do the same
* for all dests up to 'last'.
*/
stop = last;
}
}
found:
IP_VS_DBG_BUF(6, "WRR: server %s:%u "
"activeconns %d refcnt %d weight %d\n",
IP_VS_DBG_ADDR(svc->af, &dest->addr), ntohs(dest->port),
atomic_read(&dest->activeconns),
atomic_read(&dest->refcnt),
atomic_read(&dest->weight));
mark->cl = dest;
out:
write_unlock(&svc->sched_lock);
return dest;
err_noavail:
mark->cl = dest;
dest = NULL;
ip_vs_scheduler_err(svc, "no destination available");
goto out;
err_over:
mark->cl = dest;
dest = NULL;
ip_vs_scheduler_err(svc, "no destination available: "
"all destinations are overloaded");
goto out;
}
@ -212,7 +249,9 @@ static struct ip_vs_scheduler ip_vs_wrr_scheduler = {
.n_list = LIST_HEAD_INIT(ip_vs_wrr_scheduler.n_list),
.init_service = ip_vs_wrr_init_svc,
.done_service = ip_vs_wrr_done_svc,
.update_service = ip_vs_wrr_update_svc,
.add_dest = ip_vs_wrr_dest_changed,
.del_dest = ip_vs_wrr_dest_changed,
.upd_dest = ip_vs_wrr_dest_changed,
.schedule = ip_vs_wrr_schedule,
};