linux-kernel - Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Message-ID: <CAMuHMdW-sUYr8_y6av9Dbtz6JJAxBUsiTGZcK2QYEHo0x1z44w@mail.gmail.com>
Date: Wed, 28 Feb 2024 11:15:33 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>, Charlie Jenkins <charlie@...osinc.com>, 
	"Russell King (Oracle)" <linux@...linux.org.uk>, David Laight <David.Laight@...lab.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Helge Deller <deller@....de>, 
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, 
	Parisc List <linux-parisc@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Palmer Dabbelt <palmer@...osinc.com>, 
	Linux ARM <linux-arm-kernel@...ts.infradead.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, 
	KUnit Development <kunit-dev@...glegroups.com>
Subject: Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum
 and csum_ipv6_magic tests

CC testing

On Wed, Feb 28, 2024 at 8:59 AM Guenter Roeck <linux@...ck-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?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds