bonding: initial RCU conversion
This patch does the initial bonding conversion to RCU. After it the
following modes are protected by RCU alone: roundrobin, active-backup,
broadcast and xor. Modes ALB/TLB and 3ad still acquire bond->lock for
reading, and will be dealt with later. curr_active_slave needs to be
dereferenced via rcu in the converted modes because the only thing
protecting the slave after this patch is rcu_read_lock, so we need the
proper barrier for weakly ordered archs and to make sure we don't have
stale pointer. It's not tagged with __rcu yet because there's still work
to be done to remove the curr_slave_lock, so sparse will complain when
rcu_assign_pointer and rcu_dereference are used, but the alternative to use
rcu_dereference_protected would've created much bigger code churn which is
more difficult to test and review. That will be converted in time.
1. Active-backup mode
1.1 Perf recording while doing iperf -P 4
- old bonding: iperf spent 0.55% in bonding, system spent 0.29% CPU
in bonding
- new bonding: iperf spent 0.29% in bonding, system spent 0.15% CPU
in bonding
1.2. Bandwidth measurements
- old bonding: 16.1 gbps consistently
- new bonding: 17.5 gbps consistently
2. Round-robin mode
2.1 Perf recording while doing iperf -P 4
- old bonding: iperf spent 0.51% in bonding, system spent 0.24% CPU
in bonding
- new bonding: iperf spent 0.16% in bonding, system spent 0.11% CPU
in bonding
2.2 Bandwidth measurements
- old bonding: 8 gbps (variable due to packet reorderings)
- new bonding: 10 gbps (variable due to packet reorderings)
Of course the latency has improved in all converted modes, and moreover
while
doing enslave/release (since it doesn't affect tx anymore).
Also I've stress tested all modes doing enslave/release in a loop while
transmitting traffic.
Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
index 0702e91..0f539de 100644
--- a/drivers/net/bonding/bond_sysfs.c
+++ b/drivers/net/bonding/bond_sysfs.c
@@ -1243,16 +1243,16 @@
struct device_attribute *attr,
char *buf)
{
- struct slave *curr;
struct bonding *bond = to_bond(d);
+ struct slave *curr;
int count = 0;
- read_lock(&bond->curr_slave_lock);
- curr = bond->curr_active_slave;
- read_unlock(&bond->curr_slave_lock);
-
+ rcu_read_lock();
+ curr = rcu_dereference(bond->curr_active_slave);
if (USES_PRIMARY(bond->params.mode) && curr)
count = sprintf(buf, "%s\n", curr->dev->name);
+ rcu_read_unlock();
+
return count;
}
@@ -1284,7 +1284,7 @@
if (!strlen(ifname) || buf[0] == '\n') {
pr_info("%s: Clearing current active slave.\n",
bond->dev->name);
- bond->curr_active_slave = NULL;
+ rcu_assign_pointer(bond->curr_active_slave, NULL);
bond_select_active_slave(bond);
goto out;
}
@@ -1347,14 +1347,9 @@
struct device_attribute *attr,
char *buf)
{
- struct slave *curr;
struct bonding *bond = to_bond(d);
- read_lock(&bond->curr_slave_lock);
- curr = bond->curr_active_slave;
- read_unlock(&bond->curr_slave_lock);
-
- return sprintf(buf, "%s\n", curr ? "up" : "down");
+ return sprintf(buf, "%s\n", bond->curr_active_slave ? "up" : "down");
}
static DEVICE_ATTR(mii_status, S_IRUGO, bonding_show_mii_status, NULL);