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From:   "Dey, Megha" <megha.dey@intel.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>
Subject: RE: [PATCH V8 1/5] crypto: Multi-buffer encryption infrastructure
 support
Thread-Topic: [PATCH V8 1/5] crypto: Multi-buffer encryption infrastructure
 support
Thread-Index: AQHTiaT71VA7Q5Or9ESQdIw+yX/ir6N6FLYAgFlFdnuAMogJgA==
Date:   Tue, 17 Apr 2018 18:40:17 +0000
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>-----Original Message-----
>From: Herbert Xu [mailto:herbert@gondor.apana.org.au]
>Sent: Friday, March 16, 2018 7:54 AM
>To: Dey, Megha <megha.dey@intel.com>
>Cc: linux-kernel@vger.kernel.org; linux-crypto@vger.kernel.org;
>davem@davemloft.net
>Subject: Re: [PATCH V8 1/5] crypto: Multi-buffer encryption infrastructure
>support
>
>On Thu, Jan 18, 2018 at 04:44:21PM -0800, Megha Dey wrote:
>>
>> > So the mcryptd template is in fact completely superfluous.  You can
>> > remove it and just have all the main encrypt/decrypt functions
>> > invoke the underlying encrypt/decrypt function directly and achieve
>> > the same result.
>> >
>> > Am I missing something?
>>
>> Hi Herbert,
>>
>> After discussing with Tim, it seems like the mcryptd is responsible
>> for queuing up the encrypt requests and dispatching them to the actual
>> multi-buffer raw algorithm.  It also flushes the queue if we wait too
>> long without new requests coming in to force dispatch of the requests
>> in queue.
>>
>> Its function is analogous to cryptd but it has its own multi-lane
>> twists so we haven't reused the cryptd interface.
>
>I have taken a deeper look and I'm even more convinced now that mcryptd is
>simply not needed in your current model.
>
>The only reason you would need mcryptd is if you need to limit the rate of
>requests going into the underlying mb algorithm.
>
>However, it doesn't do that all.  Even though it seems to have a batch size of
>10, but because it immediately reschedules itself after the batch runs out,
>it's essentially just dumping all requests at the underlying algorithm as fast
>as they're coming in.  The underlying algorithm doesn't have need throttling
>anyway because it'll do the work when the queue is full synchronously.
>
>So why not just get rid of mcryptd completely and expose the underlying
>algorithm as a proper async skcipher/hash?

Hi Herbert,

Most part of the cryptd.c and mcryptd.c are similar, except the logic used to flush out partially completed jobs
in the case of multibuffer algorithms.

I think I will try to merge the cryptd and mcryptd adding necessary quirks for multibuffer where needed.

Also, in cryptd.c, I see shash interface being used for hash digests, update, finup, setkey etc. whereas we have shifted
to ahash interface for mcryptd. Is this correct?

Thanks,
Megha
 
>
>Thanks,
>--
>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