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

[Ben Greear <greearb@candelatech.com>]

On 08/07/2014 07:05 AM, Christian Lamparter wrote:

> The high overhead (math_state_restore and fpu_save_init) are caused by 
> the way ccm.c interacts with the aesni implementation when calculating
> the MAC [1] (in compute_mac). 
> 
>>    [ ... ]
>> 	/* now encrypt rest of data */
>> 	while (datalen >= 16) {
>> 		crypto_xor(odata, data, bs);
>> 		crypto_cipher_encrypt_one(tfm, odata, odata);
>>
>> 		datalen -= 16;
>> 		data += 16;
>> 	}
>>   [...]
> 
> crypto_cipher_encrypt_one is a wrapper which in your case calls 
> aesni's aes_encrypt [2].
> 
> And aes_encrypt looks like this: 
> 
>> 	[...]
>> 	kernel_fpu_begin();
>> 	aesni_enc(ctx, dst, src); <-- this is where it goes to _aesni_enc1
>> 	kernel_fpu_end();
>> 	[...] 
> 
> Or: for every 16 Bytes of payload there is one fpu context save and
> restore... ouch!

I have never messed with this kind of stuff...

Any idea if it would work to put the fpu_begin/end a bit higher and do all those 16 byte
chunks in a batch without messing with the FPU for each chunk?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com