On Sat, 2014-10-11 at 10:36 +0200, Heiko Carstens wrote: > 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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