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From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
To: Tom Herbert <tom@herbertland.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH net] net: Allow flow dissector to handle non 4-byte aligned headers
Date: Wed, 3 Feb 2016 12:59:47 -0500	[thread overview]
Message-ID: <20160203175947.GB14627@oracle.com> (raw)
In-Reply-To: <CALx6S37g57kSvvXQy2oY5uMixOw5t-Q2dRTRhGSYS0P=i-ff-A@mail.gmail.com>

On (02/03/16 09:51), Tom Herbert wrote:
> > (a) quite noisy
> 
> Try disabling the crash dump. That will improve performance.

huh?? 

there is no crash dump involved. If you meant "disable dump_stack()"
sure, I am aware of that, and that is the default behavior of 
log_unaligned(). I was just trying to be helpful and provide
stack traces (I dropped out quite a few, which come from mld, 
ip_fast_csum() etc, which log_unaligned rate-limits and suppresses
by default, btw)

(Removing the batteries from my fire-alarm doesnt make the fire 
go away :-))

> But as we said it's only for tunnels that specifically encapsulate an
> ethernet header with aligning it. Many other encapsulations (e.g.
> IPIP, GUE, EtherIP,IP/GRE) should be fine. We could take this to IETF
> and point out that alignment is still relevant in protocol
> development. We can't fix this for GRE or VXLAN at this point, but
> maybe there's still hope for VXLAN-GPE or Geneve...

good point about taking to ietf, but the list above is not accurate.
IP/GRE itself generated a few log_unaligned() warnings for me, I'd
have to sift through it carefully - need some time for that.. 

> Right, but there is a big difference between a performance degradation
> and a hard failure. It would at least be nice to know what the
> performance hit actually is, if it's acceptable then this would be a
> far simpler and much less invasive fix than the alternatives.

--Sowmini

      reply	other threads:[~2016-02-03 18:00 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-31 21:37 [PATCH net] net: Allow flow dissector to handle non 4-byte aligned headers Tom Herbert
2016-01-31 21:47 ` kbuild test robot
2016-01-31 22:06 ` Florian Westphal
2016-02-01  0:24 ` Eric Dumazet
2016-02-01  0:39   ` Florian Fainelli
2016-02-01 15:20     ` Nicolas Dichtel
2016-02-01 16:01       ` Sowmini Varadhan
2016-02-01  0:43   ` Sowmini Varadhan
2016-02-01 12:32 ` Sergei Shtylyov
2016-02-02  0:31 ` Sowmini Varadhan
2016-02-02  0:46   ` Tom Herbert
2016-02-02  3:56   ` Alexander Duyck
2016-02-02 13:41     ` Hannes Frederic Sowa
2016-02-02 18:35     ` Sowmini Varadhan
2016-02-03 17:07   ` Tom Herbert
2016-02-03 17:31     ` Sowmini Varadhan
2016-02-03 17:51       ` Tom Herbert
2016-02-03 17:59         ` Sowmini Varadhan [this message]

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