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

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Message-ID: <02bb92c3-a14c-4a77-a3b0-a7c857d1d60d@roeck-us.net>
Date: Tue, 27 Feb 2024 23:59:26 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
 Charlie Jenkins <charlie@...osinc.com>,
 "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: 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>
Subject: Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum
 and csum_ipv6_magic tests

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.

Guenter