After unshare test kworker hangs for ages:
$ while :; do unshare -n true; done &
$ perf report <kworker>
- 88,82% 0,00% kworker/u16:0 [kernel.vmlinux] [k] cleanup_net
cleanup_net
- ops_exit_list.isra.9
- 85,68% igmp6_net_exit
- 53,31% sock_release
- inet_release
- 25,33% rawv6_close
- ip6mr_sk_done
+ 23,38% synchronize_rcu
Keep in mind, this perf report shows the time a function was executing, and
it does not show the time, it was sleeping. But it's easy to imagine, how
much it is sleeping, if synchronize_rcu() execution takes the most time.
Top shows the kworker R time is less then 1%.
This happen, because of in ip6mr_sk_done() we do too many synchronize_rcu(),
even for the sockets, that are not referenced in mr_table, and which are not
need it. So, the progress of kworker becomes very slow.
The patch introduces apparent solution, and it makes ip6mr_sk_done() to skip
synchronize_rcu() for sockets, that are not need that. After the patch,
kworker becomes able to warm the cpu up as expected.
Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
net/ipv6/ip6mr.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 2a38f9de45d3..290a8d0d5eac 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1485,7 +1485,9 @@ int ip6mr_sk_done(struct sock *sk)
}
}
rtnl_unlock();
- synchronize_rcu();
+
+ if (!err)
+ synchronize_rcu();
return err;
}
