From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Thomas Graf <tgraf@suug.ch>,
Nikolay Aleksandrov <nikolay@redhat.com>,
"David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Ursula Braun <braunu@de.ibm.com>
Subject: [bisected] e341694e3eb5 netlink_lookup() rcu conversion causes latencies
Date: Sat, 11 Oct 2014 10:36:27 +0200 [thread overview]
Message-ID: <20141011083627.GB5074@osiris> (raw)
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...
next reply other threads:[~2014-10-11 8:36 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-11 8:36 Heiko Carstens [this message]
2014-10-11 19:32 ` [bisected] e341694e3eb5 netlink_lookup() rcu conversion causes latencies Eric Dumazet
2014-10-11 22:25 ` Thomas Graf
2014-10-11 23:08 ` David Miller
2014-10-20 8:21 ` Heiko Carstens
2014-10-20 19:53 ` [PATCH] netlink: Re-add locking to netlink_lookup() and seq walker Thomas Graf
2014-10-21 7:04 ` Heiko Carstens
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