netdev - Re: Advertise maximum number of sg supported by driver in single request

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Date:   Mon, 20 Jan 2020 10:37:12 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Ayush Sawal <ayush.sawal@...cdesigners.com>
CC:     Herbert Xu <herbert@...dor.apana.org.au>,
        <linux-crypto@...r.kernel.org>, <manojmalviya@...lsio.com>,
        Ayush Sawal <ayush.sawal@...lsio.com>, <netdev@...r.kernel.org>
Subject: Re: Advertise maximum number of sg supported by driver in single
 request

On Fri, Jan 17, 2020 at 07:08:05PM +0530, Ayush Sawal wrote:
> Hi steffen,
> 
> On 1/17/2020 5:47 PM, Steffen Klassert wrote:
> > On Fri, Jan 17, 2020 at 04:28:54PM +0530, Ayush Sawal wrote:
> > > Hi steffen,
> > > 
> > > On 1/17/2020 12:34 PM, Steffen Klassert wrote:
> > > > On Fri, Jan 17, 2020 at 12:13:07PM +0530, Ayush Sawal wrote:
> > > > > Hi Herbert,
> > > > > 
> > > > > On 1/17/2020 11:53 AM, Herbert Xu wrote:
> > > > > > On Thu, Jan 16, 2020 at 01:27:24PM +0530, Ayush Sawal wrote:
> > > > > > > The max data limit is 15 sgs where each sg contains data of mtu size .
> > > > > > > we are running a netperf udp stream test over ipsec tunnel .The ipsec tunnel
> > > > > > > is established between two hosts which are directly connected
> > > > > > Are you actually getting 15-element SG lists from IPsec? What is
> > > > > > generating an skb with 15-element SG lists?
> > > > > we have established the ipsec tunnel in transport mode using ip xfrm.
> > > > > and running traffic using netserver and netperf.
> > > > > 
> > > > > In server side we are running
> > > > > netserver -4
> > > > > In client side we are running
> > > > > "netperf -H <serverip> -p <port> -t UDP_STREAM  -Cc -- -m 21k"
> > > > > where the packet size is 21k ,which is then fragmented into 15 ip fragments
> > > > > each of mtu size.
> > > > I'm lacking a bit of context here, but this should generate 15 IP
> > > > packets that are encrypted one by one.
> > > This is what i observed ,please correct me if i am wrong.
> > > The packet when reaches esp_output(),is in socket buffer and based on the
> > > number of frags ,sg is initialized  using
> > > sg_init_table(sg,frags),where frags are 15 in our case.
> > The packet should be IP fragmented before it enters esp_output()
> > unless this is a UDP GSO packet. What kind of device do you use
> > here? Is it a crypto accelerator or a NIC that can do ESP offloads?
> 
> We have device which works as a crypto accelerator . It just encrypts the
> packets and send it back to kernel.

I just did a test and I see the same behaviour. Seems like I was
mistaken, we actually fragment the ESP packets. The only case
where we do pre-encap fragmentation is IPv6 tunnel mode. But I
wonder if it would make sense to avoid to have ESP fragments on
the wire.