Re: Looking for non-NIC hardware-offload for wpa2 decrypt.

[Christian Lamparter <chunkeey@googlemail.com>]

On Tuesday, July 29, 2014 03:50:40 PM Ben Greear wrote:
> On 07/29/2014 03:29 PM, Christian Lamparter wrote:
> > On Monday, July 28, 2014 01:50:22 PM Ben Greear wrote:
> >> On 03/31/2014 11:09 AM, Christian Lamparter wrote:
> >>> Hello,
> >>>
> >>> On Sunday, March 30, 2014 09:40:24 PM Ben Greear wrote:
> >>>> Due to hardware/firmware limitations, it does not appear possible to
> >>>> have a wifi NIC do hardware decrypt when using multiple stations on a single
> >>>> NIC (and have both stations connected to the same AP).
> >>>>
> >>>> This just happens to be one of my favourite things to do, and it kills
> >>>> performance compared to normal 'Open' throughput.
> >>>>
> >>>> I am curious if anyone knows of any way to accelerate rx-decrypt, perhaps by
> >>>> using a specialized hardware board or maybe a feature of certain CPUs?
> >>>
> >>> You could check if your CPU (bios and kernel) have support for AES-NI [0].
> >>> AFAICT mac80211 utilizes the cryptoapi. Therefore anything that supports
> >>> the proper crypto bindings can be used to accelerate the encryption and
> >>> decryption process to some degree. And it just happens that thanks to
> >>> AES-NI parts of math can be efficiently calculated by the CPU. 
> >>
> >> I recently took a look at this again, and the Intel E5 I'm using
> >> does use the aesni instructions/driver as far as I can tell.
> > Which E5 exactly? There are many different E5. 

> model name	: Intel(R) Xeon(R) CPU E5-1660 v2 @ 3.70GHz
> stepping	: 4
> microcode	: 0x427
> cpu MHz		: 2163.054
Thanks. 500Mbps should not be a issue though. At 3,70GHz one single
core should be able to encrypt/decrypt several Gbps.

> >> Throughput is still around 500Mbps where open is around 800Mbps.
> > I can't test ath10k or your multiple station on a single NIC thing. But
> > can you run a test for a "simple" single station - single AP wpa2 setup?
> > I want to know how close to the 800Mbps it actually goes.
Any data for the single station, single AP, wpa2 setup? I would like to know
what ath10k is able to achieve in this case.

> >> perf top shows this:
> >>
> >> Samples: 37K of event 'cycles', Event count (approx.): 19360716192
> >>  12.01%  [kernel]                                      [k] math_state_restore
> >>  11.64%  [kernel]                                      [k] _aesni_enc1
> >>   8.25%  [kernel]                                      [k] __save_init_fpu
> >>   2.44%  [kernel]                                      [k] crypto_xor
> >>   1.87%  [kernel]                                      [k] irq_fpu_usable
> >>   1.30%  [kernel]                                      [k] aes_encrypt
> >>   0.76%  [kernel]                                      [k] __kernel_fpu_end
> >> ....
> > Yes, aesni is doing some of the heavy lifting! But in your original post,
> > you said you are interested in accelerate rx-decrypt... Now it's about 
> > encryption offload?! [please make up your mind :-D]
> 
> The perf top results above are from receiving (and decoding) wpa2 wifi
> frames that were not decoded by the NIC because NIC rx-decrypt logic was
> disabled.  I think this means I want to accelerate the rx-decrypt.
Wait.

If you have disabled rx-decrypt logic of ath10k, then why isn't _aesni_dec1
or aes_decrypt listed in the perf top result? I think they should be. Have you
removed them from the "perf top results" or are they really absent 
altogether? 

Because, from this perf result, it looks like your CPU is not burden by the
incoming RX at all?! Instead it is busy with the encryption of frames
it will be transmitting (in case of tcp, this could be tcp acks).

It could be that I missed something important about the setup.
For example, I assumed that you have a dedicated 802.11ac AP
and the perf results are coming from the E5 machine with the ath10k
in multi-station mode. The AP would be transmitting, whereas
the E5 would be receiving. Is this assumption correct or not?

> Transmit is not a problem for me because I can make the NIC do the
> encryption in it's hardware.

> Thanks for the suggestions below.  I have managed to find yet another
> way to crash my firmware so I have to pay attention to that for a bit,
> but will look into that decrypt code in more detail when I get a chance.

Yeah, but don't bother with the suggestions. Johannes pointed out "that
this would be mostly useless afaict as the list is only iterated if you have
software fragmentation." Furthermore, they only covered the ENcryption 
process of the TX path and not the DEcryption part of the RX path (which
is what you are interested in).

Regards
Christian