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Subject: Re: [PATCH v8 4/8] crypto: caam - simplify RNG implementation
To:     Andrey Smirnov <andrew.smirnov@gmail.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>
Cc:     Chris Healy <cphealy@gmail.com>,
        Lucas Stach <l.stach@pengutronix.de>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Iuliana Prodan <iuliana.prodan@nxp.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>
References: <20200316150047.30828-1-andrew.smirnov@gmail.com>
 <20200316150047.30828-5-andrew.smirnov@gmail.com>
From:   =?UTF-8?Q?Horia_Geant=c4=83?= <horia.geanta@nxp.com>
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Date:   Tue, 17 Mar 2020 23:37:32 +0200
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On 3/16/2020 5:01 PM, Andrey Smirnov wrote:
> Rework CAAM RNG implementation as follows:
> 
> - Make use of the fact that HWRNG supports partial reads and will
> handle such cases gracefully by removing recursion in caam_read()
> 
> - Convert blocking caam_read() codepath to do a single blocking job
> read directly into requested buffer, bypassing any intermediary
> buffers
> 
> - Convert async caam_read() codepath into a simple single
> reader/single writer FIFO use-case, thus simplifying concurrency
> handling and delegating buffer read/write position management to KFIFO
> subsystem.
> 
> - Leverage the same low level RNG data extraction code for both async
> and blocking caam_read() scenarios, get rid of the shared job
> descriptor and make non-shared one as a simple as possible (just
> HEADER + ALGORITHM OPERATION + FIFO STORE)
> 
> - Split private context from DMA related memory, so that the former
> could be allocated without GFP_DMA.
> 
> NOTE: On its face value this commit decreased throughput numbers
> reported by
> 
>   dd if=/dev/hwrng of=/dev/null bs=1 count=100K [iflag=nonblock]
> 
> by about 15%, however commits that enable prediction resistance and
> limit JR total size impact the performance so much and move the
> bottleneck such as to make this regression irrelevant.
> 
> NOTE: On the bright side, this commit reduces RNG in kernel DMA buffer
> memory usage from 2 x RN_BUF_SIZE (~256K) to 32K.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> Cc: Chris Healy <cphealy@gmail.com>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Horia Geantă <horia.geanta@nxp.com>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: Iuliana Prodan <iuliana.prodan@nxp.com>
> Cc: linux-crypto@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-imx@nxp.com
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>

Thanks,
Horia