Messages in this thread | | | Date | Sat, 11 Oct 2014 10:36:27 +0200 | From | Heiko Carstens <> | Subject | [bisected] e341694e3eb5 netlink_lookup() rcu conversion causes latencies |
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Hi all,
it just came to my attention that commit e341694e3eb5 "netlink: Convert netlink_lookup() to use RCU protected hash table" causes network latencies for me on s390.
The testcase is quite simple and 100% reproducible on s390:
Simply login via ssh to a remote system which has the above mentioned patch applied. Any action like pressing return now has significant latencies. Or in other words, working via such a connection becomes a pain ;)
I haven't debugged it, however I assume the problem is that a) the commit introduces a synchronize_net() call und b) s390 kernels usually get compiled with CONFIG_HZ_100 while most other architectures use CONFIG_HZ_1000. If I change the kernel config to CONFIG_HZ_1000 the problem goes away, however I don't consider this a fix...
Another reason why this hasn't been observed on x86 may or may not be that we haven't implemented CONFIG_HAVE_CONTEXT_TRACKING on s390 (yet). But that's just guessing...
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