> From: Tyler Retzlaff [mailto:roret...@linux.microsoft.com] > Sent: Thursday, 25 January 2024 19.37 > > ping. > > Please review this thread if you have time, the main point of > discussion > I would like to receive consensus on the following questions. > > 1. Should we continue to expand common alignments behind an __rte_macro > > i.e. what do we prefer to appear in code > > alignas(RTE_CACHE_LINE_MIN_SIZE) > > -- or -- > > __rte_cache_aligned > > One of the benefits of dropping the macro is it provides a clear visual > indicator that it is not placed in the same location or get applied > to types as is done with __attribute__((__aligned__(n))).
We don't want our own proprietary variant of something that already exists in the C standard. Now that we have moved to C11, the __rte alignment macros should be considered obsolete. Note: I don't mind convenience macros for common use cases, so we could also introduce the macro suggested by Mattias [1]: #define RTE_CACHE_ALIGNAS alignas(RTE_CACHE_LINE_SIZE) [1]: https://inbox.dpdk.org/dev/dc3f3131-38e6-4219-861e-b31ec10c0...@lysator.liu.se/ > > 2. where should we place alignas(n) or __rte_macro (if we use a macro) > > Should it be on the same line as the variable or field or on the > preceeding line? > > /* same line example struct */ > struct T { > /* alignas(64) applies to field0 *not* struct T type declaration > */ > alignas(64) void *field0; > void *field1; > > ... other fields ... > > alignas(64) uint64_t field5; > uint32_t field6; > > ... more fields ... > > }; > > /* same line example array */ > alignas(64) static const uint32_t array[4] = { ... }; > > -- or -- > > /* preceeding line example struct */ > struct T { > /* alignas(64) applies to field0 *not* struct T type declaration > */ > alignas(64) > void *field0; > void *field1; > > ... other fields ... > > alignas(64) > uint64_t field5; > uint32_t field6; > > ... more fields ... > > }; > > /* preceeding line example array */ > alignas(64) > static const uint32_t array[4] = { ... }; > Searching the net for what other projects do, I came across this required placement [2]: uint64_t alignas(64) field5; [2]: https://lore.kernel.org/buildroot/20230730000851.6faa3391@windsurf/T/ So let's follow the standard's intention and put them on the same line. On an case-by-case basis, we can wrap lines if it improves readability, like we do with function headers that have a lot of attributes. > > I'll submit patches for lib/* once the discussion is concluded. > > thanks folks
