From: Casey Schaufler <casey@schaufler-ca•com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: David Miller <davem@davemloft•net>,
pmoore@redhat•com, netdev@vger•kernel.org, mvadkert@redhat•com,
selinux@tycho•nsa.gov, linux-security-module@vger•kernel.org,
Casey Schaufler <casey@schaufler-ca•com>
Subject: Re: [PATCH] tcp: assign the sock correctly to an outgoing SYNACK packet
Date: Mon, 08 Apr 2013 17:59:59 -0700 [thread overview]
Message-ID: <5163680F.4030200@schaufler-ca.com> (raw)
In-Reply-To: <1365467636.3887.67.camel@edumazet-glaptop>
On 4/8/2013 5:33 PM, Eric Dumazet wrote:
> On Mon, 2013-04-08 at 16:40 -0700, Casey Schaufler wrote:
>
>> OK, let's do the math.
>>
>> First off, it's 4 bytes, not 8. It replaces the secmark.
>> Your increased memory usage is going to be
>>
>> 4 bytes/packet * M packets/second * N seconds
>>
>> Where M is the rate at which you're processing packets and
>> N is the length of time it takes to process a packet.
>>
>> Let's pretend we have an embedded system that does nothing but send
>> 128 byte packets on a 10Gb port. That's 10M packets/second. If it
>> takes a full second to process a packet the overhead is 40MB for that
>> second. I have it on good authority that packets can be processed
>> in considerably less time than that. The real number is more like
>> 0.05 seconds. That means your actual overhead is more like 1MB.
>>
>> These are dumbed down calculations. I am not a memory usage expert.
>> I am convinced that "real" calculations are going to get similar
>> numbers. I am, of course, willing to be swayed by evidence that I
>> am wrong.
>>
>> Compare that to the overhead associated with using CIPSO on packets
>> that never leave the box.
> Maths are not that simple,
I am willing to accept that. I am willing to be
educated. I would be interested to see what the
"real" maths are, and how far off my dumb version
might actually be.
> and its not about size of sk_buff, since the
> number of in-flight skb should be quite small.
The reason we're told that there can't be a blob
pointer in the sk_buff is that it increases the size
of the sk_buff. Yes, it *is* about the size.
> Its the time to init this memory for _every_ packet.
Which is a function of the size, no?
> sizeof(sk_buff) is 0xf8, very close to cross the 256 bytes limit.
0xf8 + 0x4 = 0xfc
248 + 4 = 252
> Add a single _byte_ and it becomes a matter of adding a _cache_ line,
> and thats 25 % cost, assuming 64bytes cache lines.
I don't see that with adding 4 bytes. Again, I'm willing to be
educated if I'm wrong.
> So instead of processing 10M packets per second, we would process 9M
> packets per second, or maybe less.
>
> Yes, 256 bytes per sk_buff, this is the current insane situation.
> (Not counting the struct skb_shared_info, adding at least one additional
> cache line)
Sorry, but I don't see what's insane with either the
current 248 byte sk_buff or a 252 byte sk_buff.
As always, I am willing to be educated.
Thank you.
next prev parent reply other threads:[~2013-04-09 0:59 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-08 15:45 [PATCH] tcp: assign the sock correctly to an outgoing SYNACK packet Paul Moore
2013-04-08 16:14 ` David Miller
2013-04-08 17:22 ` Paul Moore
2013-04-08 17:36 ` Eric Dumazet
2013-04-08 17:40 ` Paul Moore
2013-04-08 17:47 ` Eric Dumazet
2013-04-08 18:01 ` Eric Dumazet
2013-04-08 18:12 ` Paul Moore
2013-04-08 18:21 ` Eric Dumazet
2013-04-08 18:26 ` Paul Moore
2013-04-08 18:34 ` Eric Dumazet
2013-04-08 18:30 ` Eric Dumazet
2013-04-08 20:37 ` Paul Moore
2013-04-08 20:44 ` David Miller
2013-04-08 20:53 ` Paul Moore
2013-04-08 20:55 ` Eric Dumazet
2013-04-08 21:09 ` Paul Moore
2013-04-08 21:14 ` David Miller
2013-04-08 21:17 ` Eric Dumazet
2013-04-09 3:58 ` [PATCH] selinux: add a skb_owned_by() hook Eric Dumazet
2013-04-09 4:29 ` Casey Schaufler
2013-04-09 4:41 ` David Miller
2013-04-09 5:14 ` Casey Schaufler
2013-04-09 11:39 ` Paul Moore
2013-04-09 6:24 ` Eric Dumazet
2013-04-09 11:45 ` Paul Moore
2013-04-09 7:38 ` James Morris
2013-04-09 12:06 ` Paul Moore
2013-04-09 17:23 ` David Miller
2013-04-08 18:32 ` [PATCH] tcp: assign the sock correctly to an outgoing SYNACK packet Paul Moore
2013-04-08 21:10 ` Paul Moore
2013-04-08 21:15 ` David Miller
2013-04-08 21:24 ` Paul Moore
2013-04-08 21:33 ` David Miller
2013-04-08 22:01 ` Paul Moore
2013-04-08 22:08 ` David Miller
2013-04-08 23:40 ` Casey Schaufler
2013-04-09 0:33 ` Eric Dumazet
2013-04-09 0:59 ` Casey Schaufler [this message]
2013-04-09 1:09 ` Eric Dumazet
2013-04-09 1:24 ` Casey Schaufler
2013-04-09 13:19 ` Paul Moore
2013-04-09 13:33 ` Paul Moore
2013-04-09 14:00 ` Eric Dumazet
2013-04-09 14:19 ` Paul Moore
2013-04-09 14:31 ` Eric Dumazet
2013-04-09 14:52 ` Paul Moore
2013-04-09 15:05 ` Paul Moore
2013-04-09 15:07 ` Eric Dumazet
2013-04-09 15:17 ` Paul Moore
2013-04-09 15:32 ` Eric Dumazet
2013-04-09 15:57 ` Paul Moore
2013-04-09 16:11 ` Casey Schaufler
2013-04-09 16:56 ` David Miller
2013-04-09 17:00 ` Paul Moore
2013-04-09 17:09 ` David Miller
2013-04-09 17:10 ` David Miller
2013-04-09 14:05 ` Ben Hutchings
2013-04-09 14:10 ` Paul Moore
2013-04-08 21:34 ` Ben Hutchings
2013-04-08 19:25 ` David Miller
2013-04-08 16:19 ` Eric Dumazet
2013-04-08 18:03 ` Sergei Shtylyov
2013-04-08 18:12 ` Paul Moore
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