linux-kernel - Re: [PATCH v2 2/4] crypto: exynos

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 12 Dec 2017 15:49:47 +0100
From:   Łukasz Stelmach <l.stelmach@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     robh+dt@...nel.org, Stephan Mueller <smueller@...onox.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Kukjin Kim <kgene@...nel.org>, linux-crypto@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2 2/4] crypto: exynos - Improve performance of PRNG

It was <2017-12-11 pon 15:54>, when Krzysztof Kozlowski wrote:
> On Mon, Dec 11, 2017 at 3:06 PM, Łukasz Stelmach <l.stelmach@...sung.com> wrote:
>> Cc: Marek Szyprowski <m.szyprowski@...sung.com>, Bartlomiej
>> Zolnierkiewicz <b.zolnierkie@...sung.com>
>
> This should not appear here.

A glitch in a scripted invocation of git-format-patch, fixed.

>> Use memcpy_fromio() instead of custom exynos_rng_copy_random() function
>> to retrieve generated numbers from the registers of PRNG.
>>
>> Rearrange the loop around cpu_relax(). In a loop with while() at the
>> beginning and the cpu_relax() removed the retry variable is decremented
>> twice (down to 98).
>
> I had troubles with understanding this sentence... and then I figured
> out that you are referring to some case without cpu_relax(). I do not
> see how it is relevant to this case. Compare the new code with old,
> not with some imaginary case without barriers (thus maybe reordered?).
>
> Your solution is strictly performance oriented so it would be nice to
> see here the exact difference in numbers justifying the change. But
> only the change for while() -> do-while(), not mixed with
> memcpy_fromio.

Apparently, after trhough tests, I must admit, the way the status
register is being polled is insignificant for the performance. I will
remove from the patch any changes in the loop.

It is the way, the random bytes are copied from the regiesteres, that
makes the difference (5.9 MB/s vs 7.1 MB/s)

Thank you very much for your assistance in reaching this conclusion.

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

Download attachment "signature.asc" of type "application/pgp-signature" (473 bytes)