linux-kernel - Re: [EXTERNAL] Re: [EXTERNAL] Re: [PATCH v2 0/6] Add support for Texas Instruments MCRC64 engine

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Date:   Wed, 20 Sep 2023 12:23:25 +0530
From:   Kamlesh Gurudasani <kamlesh@...com>
To:     Eric Biggers <ebiggers@...nel.org>
CC:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tero Kristo <kristo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        <linux-crypto@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [EXTERNAL] Re: [EXTERNAL] Re: [PATCH v2 0/6] Add support for
 Texas Instruments MCRC64 engine

Kamlesh Gurudasani <kamlesh@...com> writes:
...

> Hi Eric, thanks for your detailed and valuable inputs.
>
> As per your suggestion, we did some profiling. 
>
> Use case is to calculate crc32/crc64 for file input from user space.
>
> Instead of directly implementing PMULL based CRC64, we made first comparison between 
> Case 1.
> CRC32 (splice() + kernel space SW driver) 
> https://gist.github.com/ti-kamlesh/5be75dbde292e122135ddf795fad9f21
>
> Case 2.
> CRC32(mmap() + userspace armv8 crc32 instruction implementation)
> (tried read() as well to get contents of file, but that lost to mmap() so not mentioning number here)
> https://gist.github.com/ti-kamlesh/002df094dd522422c6cb62069e15c40d
>
> Case 3.
> CRC64 (splice() + MCRC64 HW)
> https://gist.github.com/ti-kamlesh/98b1fc36c9a7c3defcc2dced4136b8a0
>
>
> Overall, overhead of userspace + af_alg + driver in (Case 1) and
> ( Case 3) is ~0.025s, which is constant for any file size.
> This is calculated using real time to calculate crc  -
> driver time (time spend inside init() + update() +final()) = overhead ~0.025s    
>
>
>
> +-------------------+-----------------------------+-----------------------+------------------------+------------------------+
> |                   |                             |                       |                        |                        |
> | File size         | 120mb(ideal size for us)    | 20mb                  | 15mb                   | 5mb                    |
> +===================+=============================+=======================+========================+========================+
> |                   |                             |                       |                        |                        |
> | CRC32 (Case 1)    | Driver time 0.155s          | Driver time 0.0325s   | Driver time 0.019s     | Driver time 0.0062s    |
> |                   |    real time 0.18s          |    real time 0.06s    |    real time 0.04s     |    real time 0.03s     |
> |                   |    overhead 0.025s          |    overhead 0.025s    |    overhead 0.021s     |    overhead ~0.023s    |
> +-------------------+-----------------------------+-----------------------+------------------------+------------------------+
> |                   |                             |                       |                        |                        |
> | CRC32 (Case 2)    | Real time 0.30s             | Real time 0.05s       | Real time 0.04s        | Real time 0.02s        |
> +-------------------+-----------------------------+-----------------------+------------------------+------------------------+
> |                   |                             |                       |                        |                        |
> | CRC64 (Case 3)    | Driver time   0.385s        | Driver time 0.0665s   | Driver time 0.0515s    | Driver time 0.019s     |
> |                   |    real time 0.41s          |    real time 0.09s    |    real time 0.08s     |    real time 0.04s     |
> |                   |    overhead 0.025s          |    overhead 0.025s    |    overhead ~0.025s    |    overhead ~0.021s    |
> +-------------------+-----------------------------+-----------------------+------------------------+------------------------+
>
> Here, if we consider similar numbers for crc64 PMULL implementation as
> crc32 (case 2) , we save good number of cpu cycles using mcrc64
> in case of files bigger than 5-10mb as most of the time is being spent in HW offload.
>
> Regards,
> Kamlesh

Hi Eric,

Please let me know if above numbers make sense to you and I should send
next revision.

Regards,
Kamlesh