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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Fri, 14 Oct 2016 12:11:12 +0100
Message-ID: <CAKv+Gu9t2fk2+4QwsDATv11wggQPryobGUGJQHO-G09bYbecGg@mail.gmail.com>
Subject: Re: [mac80211] BUG_ON with current -git (4.8.0-11417-g24532f7)
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Andy Lutomirski <luto@amacapital.net>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        "linux-next@vger.kernel.org" <linux-next@vger.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Network Development <netdev@vger.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Linux Wireless List <linux-wireless@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jouni Malinen <j@w1.fi>
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Sender: linux-kernel-owner@vger.kernel.org
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On 14 October 2016 at 11:00, Johannes Berg <johannes@sipsolutions.net> wrote:
>
>> So why is the performance hit acceptable for ESP but not for WPA? We
>> could easily implement the same thing, i.e.,
>> kmalloc(GFP_ATOMIC)/kfree the aead_req struct rather than allocate it
>> on the stack
>
> Yeah, maybe we should. It's likely a much bigger allocation, but I
> don't actually know if that affects speed.
>
> In most cases where you want high performance we never hit this anyway
> since we'll have hardware crypto. I know for our (Intel's) devices we
> normally never hit these code paths.
>
> But on the other hand, you also did your changes for a reason, and the
> only reason I can see of that is performance. So you'd be the one with
> most "skin in the game", I guess?
>

Well, what sucks here is that the accelerated driver I implemented for
arm64 does not actually need this, as long as we take aad[] off the
stack. And note that the API was changed since my patch, to add aad[]
to the scatterlist: prior to this change, it used
aead_request_set_assoc() to set the associated data separately.