From: Rick Jones <rick.jones2@hp.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Tom Parkin <tparkin@katalix.com>,
netdev@vger.kernel.org, David.Laight@ACULAB.COM,
James Chapman <jchapman@katalix.com>
Subject: Re: [PATCH v2] l2tp: use per-cpu variables for u64_stats updates
Date: Wed, 27 Jun 2012 13:21:56 -0700 [thread overview]
Message-ID: <4FEB6B64.5060708@hp.com> (raw)
In-Reply-To: <1340823810.26242.81.camel@edumazet-glaptop>
On 06/27/2012 12:03 PM, Eric Dumazet wrote:
> On Wed, 2012-06-27 at 13:00 +0100, Tom Parkin wrote:
>> This patch fixes a race condition in l2tp when updating tunnel and
>> session statistics. Previously it was possible for multiple threads
>> to concurrently call u64_stats_update*(), which lead to statistics
>> readers blocking forever.
>>
>> This race was discovered on an AMD64 SMP machine running a 32bit
>> kernel. Running "ip l2tp" while sending data over an Ethernet
>> pseudowire resulted in an occasional soft lockup in
>> u64_stats_fetch_begin() called from l2tp_nl_session_send().
>>
>> For safe lockless update of l2tp stats, data is now stored in per-cpu
>> variables. These per-cpu datasets are then summed at read time via.
>> an extra helper function l2tp_stats_copy() which has been added to
>> l2tp_core.c.
>>
>
> Do we really need 64bits stats on 32bit arches for l2tp ?
It is a question of the speed of the communications more than the
bitness of the processor no?
rick jones
next prev parent reply other threads:[~2012-06-27 20:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-27 12:00 [PATCH v2] l2tp: use per-cpu variables for u64_stats updates Tom Parkin
2012-06-27 19:03 ` Eric Dumazet
2012-06-27 20:21 ` Rick Jones [this message]
2012-06-27 20:39 ` Eric Dumazet
2012-06-27 20:50 ` Stephen Hemminger
2012-06-27 20:58 ` Ben Greear
2012-06-27 21:20 ` Eric Dumazet
2012-06-27 21:31 ` Ben Greear
2012-06-27 21:35 ` Eric Dumazet
2012-06-27 23:01 ` Rick Jones
2012-06-27 23:09 ` David Miller
2012-06-27 23:39 ` Rick Jones
2012-06-28 5:00 ` Eric Dumazet
2012-06-28 8:24 ` Tom Parkin
2012-06-28 8:46 ` David Laight
2012-06-28 18:17 ` Ben Hutchings
2012-06-27 21:32 ` Eric Dumazet
2012-06-27 21:40 ` Ben Greear
2012-06-27 21:50 ` Eric Dumazet
2012-06-27 21:00 ` Rick Jones
2012-06-27 22:21 ` David Miller
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