| Message ID | 20200917221922.A5D3D95C0A57@us180.sjc.aristanetworks.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] net: use exponential backoff in netdev_wait_allrefs | expand |
From: fruggeri@arista.com (Francesco Ruggeri) Date: Thu, 17 Sep 2020 15:19:22 -0700 > static void netdev_wait_allrefs(struct net_device *dev) > { > unsigned long rebroadcast_time, warning_time; > int refcnt; > + unsigned int wait = MIN_MSLEEP; Please preserve the reverse christmas tree ordering of local variables here, thank you.
diff --git a/net/core/dev.c b/net/core/dev.c index 4086d335978c..69f549780b8e 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -9986,10 +9986,13 @@ EXPORT_SYMBOL(netdev_refcnt_read); * We can get stuck here if buggy protocols don't correctly * call dev_put. */ +#define MIN_MSLEEP ((unsigned int)16) +#define MAX_MSLEEP ((unsigned int)250) static void netdev_wait_allrefs(struct net_device *dev) { unsigned long rebroadcast_time, warning_time; int refcnt; + unsigned int wait = MIN_MSLEEP; linkwatch_forget_dev(dev); @@ -10023,7 +10026,8 @@ static void netdev_wait_allrefs(struct net_device *dev) rebroadcast_time = jiffies; } - msleep(250); + msleep(wait); + wait = min(wait << 1, MAX_MSLEEP); refcnt = netdev_refcnt_read(dev);
The combination of aca_free_rcu, introduced in commit 2384d02520ff ("net/ipv6: Add anycast addresses to a global hashtable"), and fib6_info_destroy_rcu, introduced in commit 9b0a8da8c4c6 ("net/ipv6: respect rcu grace period before freeing fib6_info"), can result in an extra rcu grace period being needed when deleting an interface, with the result that netdev_wait_allrefs ends up hitting the msleep(250), which is considerably longer than the required grace period. This can result in long delays when deleting a large number of interfaces, and it can be observed with this script: ns=dummy-ns NIFS=100 ip netns add $ns ip netns exec $ns ip link set lo up ip netns exec $ns sysctl net.ipv6.conf.default.disable_ipv6=0 ip netns exec $ns sysctl net.ipv6.conf.default.forwarding=1 for ((i=0; i<$NIFS; i++)) do if=eth$i ip netns exec $ns ip link add $if type dummy ip netns exec $ns ip link set $if up ip netns exec $ns ip -6 addr add 2021:$i::1/120 dev $if done for ((i=0; i<$NIFS; i++)) do if=eth$i ip netns exec $ns ip link del $if done ip netns del $ns This patch uses exponential backoff instead of the fixed msleep(250) to get out of the loop faster. Time with this patch on a 5.4 kernel: real 0m8.199s user 0m0.402s sys 0m1.213s Time without this patch: real 0m31.522s user 0m0.438s sys 0m1.156s v2: use exponential backoff instead of trying to wake up netdev_wait_allrefs. Signed-off-by: Francesco Ruggeri <fruggeri@arista.com> --- net/core/dev.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)