From: Eric Dumazet <eric.dumazet@gmail.com>
To: Heiko Carstens <heiko.carstens@de.ibm.com>,
Sasha Levin <sasha.levin@oracle.com>,
paulmck@linux.vnet.ibm.com
Cc: Thomas Graf <tgraf@suug.ch>,
Nikolay Aleksandrov <nikolay@redhat.com>,
"David S. Miller" <davem@davemloft.net>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Ursula Braun <braunu@de.ibm.com>
Subject: Re: [bisected] e341694e3eb5 netlink_lookup() rcu conversion causes latencies
Date: Sat, 11 Oct 2014 12:32:44 -0700 [thread overview]
Message-ID: <1413055964.9362.50.camel@edumazet-glaptop2.roam.corp.google.com> (raw)
In-Reply-To: <20141011083627.GB5074@osiris>
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...
CC Paul and Sasha
next prev parent reply other threads:[~2014-10-11 19:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-11 8:36 [bisected] e341694e3eb5 netlink_lookup() rcu conversion causes latencies Heiko Carstens
2014-10-11 19:32 ` Eric Dumazet [this message]
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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