linux-kernel - Re: [PATCH] lfsr: a simple binary Galois linear feedback shift register

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Message-ID: <551B1E78.1040000@hp.com>
Date:	Tue, 31 Mar 2015 18:23:52 -0400
From:	Waiman Long <waiman.long@...com>
To:	Shuah Khan <shuahkh@....samsung.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH] lfsr: a simple binary Galois linear feedback shift register

On 03/31/2015 05:58 PM, Shuah Khan wrote:
> On 03/31/2015 03:53 PM, Waiman Long wrote:
>> On 03/31/2015 03:21 PM, Shuah Khan wrote:
>>> On 03/31/2015 11:28 AM, Waiman Long wrote:
>>>> This patch is based on the code sent out by Peter Zijstra as part
>>>> of his queue spinlock patch to provide a hashing function with open
>>>> addressing.  The lfsr() function can be used to return a sequence of
>>>> numbers that cycle through all the bit patterns (2^n -1) of a given
>>>> bit width n except the value 0 in a somewhat random fashion depending
>>>> on the LFSR tap that is being used.
>>> Does this new test intended to test a new kernel feature? If so could
>>> you please include what it tests in the commit log. It isn't very clear
>>> to me what this test does?
>>>
>> This test is for checking the correctness of the lfsr.h header file. I
>> will clarify that in the commit log.
>>
>>>> This code should be a standalone patch and not part of a larger
>>>> patch series.  I have also modified and extended it and added some
>>>> testing code to verify the correctness of the taps that are being used.
>>> The above can be left out of the commit log.
>>>
>> Sure.
>>
>>>> Signed-off-by: Waiman Long<Waiman.Long@...com>
>>>> ---
>>>>    include/linux/lfsr.h                     |   84
>>>> ++++++++++++++++++++++++++++++
>>>>    tools/testing/selftests/lfsr/Makefile    |   11 ++++
>>>>    tools/testing/selftests/lfsr/test-lfsr.c |   70
>>>> +++++++++++++++++++++++++
>>>>    3 files changed, 165 insertions(+), 0 deletions(-)
>>>>    create mode 100644 include/linux/lfsr.h
>>>>    create mode 100644 tools/testing/selftests/lfsr/Makefile
>>>>    create mode 100644 tools/testing/selftests/lfsr/test-lfsr.c
>>> I don't see the test added to selftests/Makefile? Is it the intent
>>> to leave it out of default test run and install? If this test
>>> is intended to be part of selftests run and install, please add
>>> it to selftests Makefile and also add install target support.
>>> You can find good examples in linux-kselftest next branch.
>>> Please add a .gitignore for git to ignore the binaries built.
>>>
>>> thanks,
>>> -- Shuah
>>>
>>>
>> Yes, it is intended to be left out of the default selftest run and
>> install because the lfsr.h header is for kernel internal use and is not
>> accessible from any of the kernel syscall APIs.
>>
> Please add this to the commit log as well that it shouldn't be included
> in the default run and install. Also BUG_ON and BUILD_BUG_ON are used
> in this test. These are kernel defines, hope these are included somehow.
>
> -- Shuah
>

I will update the patch once I receive feedbacks from others. The lfsr.h 
header does use BUG_ON and BUILD_BUG_ON, but they are disabled in the 
self-test.

-Longman
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