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Date: Wed, 28 Feb 2024 07:40:43 -0800
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Subject: Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum
 and csum_ipv6_magic tests
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To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>,
 Charlie Jenkins <charlie@rivosinc.com>,
 "Russell King (Oracle)" <linux@armlinux.org.uk>,
 David Laight <David.Laight@aculab.com>, Palmer Dabbelt <palmer@dabbelt.com>,
 Andrew Morton <akpm@linux-foundation.org>, Helge Deller <deller@gmx.de>,
 "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
 Parisc List <linux-parisc@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 Palmer Dabbelt <palmer@rivosinc.com>,
 Linux ARM <linux-arm-kernel@lists.infradead.org>,
 "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>,
 KUnit Development <kunit-dev@googlegroups.com>
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From: Guenter Roeck <linux@roeck-us.net>
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On 2/28/24 02:15, Geert Uytterhoeven wrote:
> CC testing
> 
> On Wed, Feb 28, 2024 at 8:59 AM Guenter Roeck <linux@roeck-us.net> wrote:
>> On 2/27/24 23:25, Christophe Leroy wrote:
>> [ ... ]
>>>>
>>>> This test case is supposed to be as true to the "general case" as
>>>> possible, so I have aligned the data along 14 + NET_IP_ALIGN. On ARM
>>>> this will be a 16-byte boundary since NET_IP_ALIGN is 2. A driver that
>>>> does not follow this may not be appropriately tested by this test case,
>>>> but anyone is welcome to submit additional test cases that address this
>>>> additional alignment concern.
>>>
>>> But then this test case is becoming less and less true to the "general
>>> case" with this patch, whereas your initial implementation was almost
>>> perfect as it was covering most cases, a lot more than what we get with
>>> that patch applied.
>>>
>> NP with me if that is where people want to go. I'll simply disable checksum
>> tests on all architectures which don't support unaligned accesses (so far
>> it looks like that is only arm with thumb instructions, and possibly nios2).
>> I personally find that less desirable and would have preferred a second
>> configurable set of tests for unaligned accesses, but I have no problem
>> with it.
> 
> IMHO the tests should validate the expected functionality.  If a test
> fails, either functionality is missing or behaves wrong, or the test
> is wrong.
> 
> What is the point of writing tests for a core functionality like network
> checksumming that do not match the expected functionality?
> 

Tough one. I can't enable CONFIG_NET_TEST on nios2, parisc, and arm with THUMB
enabled due to crashes or hangs in gso tests. I accept that. Downside is that I
have to disable CONFIG_NET_TEST on those architectures/platforms entirely,
meaning a whole class of tests are missing for those architectures. I would
prefer to have a configuration option such as CONFIG_NET_GSO_TEST to let me
disable the problematic tests for the affected platforms so I can run all
the other network unit tests. Yes, obviously something is wrong either with
the affected tests or with the implementation of the tested functionality
on the affected systems, but that could be handled separately if a separate
configuration option existed, and new regressions in other tests on the affected
architectures could be identified as they happen.

This case is similar. I'd prefer to have a separate configuration option,
say, CONFIG_CHECKSUM_MISALIGNED_KUNIT, which I can disable to be able to
run the common checksum tests on platforms / architectures which don't
support unaligned accesses.

However, as I said, if the community wants to take a harsh stance, I have no
problem with just disabling groups of tests entirely on platforms which have
a problem with part of it.

Guenter