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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Ben Greear <greearb@candelatech.com>
Cc: Stephen Hemminger <shemminger@vyatta.com>,
	Rick Jones <rick.jones2@hp.com>, 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 23:35:47 +0200	[thread overview]
Message-ID: <1340832947.26242.169.camel@edumazet-glaptop> (raw)
In-Reply-To: <4FEB7BB9.1080905@candelatech.com>

On Wed, 2012-06-27 at 14:31 -0700, Ben Greear wrote:

> For an example, see the VLAN code. rx-errors and tx-dropped are only 32-bit
> counters.  Now, in the real world, we wouldn't expect those counters to
> increase at high rates, but they are still 32-bit counters masquerading
> as 64, and they could wrap after a while, so any code that expected a wrap
> to mean a 64-bit wrap would be wrong.
> 
> At the time I was last complaining, there were lots more cases
> of this that I was fighting with, but I don't recall exactly what they
> were.  Once my user-space code got paranoid enough, it was able to
> at least mostly deal with 32 and 64 wraps.

Good, you now know how to deal correctly with these things.

Using 64bit fields for tx_dropped is what I call kernel bloat.

If only all drops were correctly accounted...

I believe 50% of drivers are buggy in this aspect.

  reply	other threads:[~2012-06-27 21:35 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
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 [this message]
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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