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Date:   Wed, 2 Dec 2020 10:30:24 +1100
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Ben Greear <greearb@candelatech.com>,
        Steve deRosier <derosier@cal-sierra.com>
Subject: Re: [PATCH v2] crypto: aesni - add ccm(aes) algorithm implementation
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On Wed, Dec 02, 2020 at 12:24:47AM +0100, Ard Biesheuvel wrote:
>
> True. But the fallback only gets executed if the scheduler is stupid
> enough to schedule the TX task onto the core that is overloaded doing
> RX softirqs. So in the general case, both TX and RX will be using
> AES-NI instructions (unless the CCMP is done in hardware which is the
> most common case by far)

I don't think this makes sense.  TX is typically done in response
to RX so the natural alignment is for it to be on the same CPU.
 
> Wireless is very different. Wifi uses a medium that is fundamentally
> shared, and so the load it can induce is bounded. There is no way a
> wifi interface is going to saturate a 64-bit AES-NI core doing CCMP in
> software.

This sounds pretty tenuous.  In any case, even if wireless itself
doesn't get you, there could be loads running on top of it, for
example, IPsec.

> Given the above, can't we be pragmatic here? This code addresses a
> niche use case, which is not affected by the general concerns
> regarding async crypto.

We already have a framework for acceleration that works properly
in aesni, I don't want to see us introduce another broken model
within the same driver.

So either just leave the whole thing along or do it properly by
making wireless async.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt