On Thu, Jan 25, 2024 at 11:53:04PM +0100, Morten Brørup wrote: > > 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]:
ack > > #define RTE_CACHE_ALIGNAS alignas(RTE_CACHE_LINE_SIZE) > > [1]: > https://inbox.dpdk.org/dev/dc3f3131-38e6-4219-861e-b31ec10c0...@lysator.liu.se/ i'm good with this, it satisfies that it is a different name than the original and therefore achieves the same intent. i'll spin the patch series with this macro. > > > > > 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. just fyi. the linked code is c++ and standard c++ has both semantic and syntactic differences from standard c. notably standard c is moving away from the notion that you can alignas types and instead you align variables/fields/members. further restricting placement is the need to choose an intersecting placement that works when consumed in either a c or c++ translation unit. so the options i present above are that intersection. ty > > > > > > I'll submit patches for lib/* once the discussion is concluded. > > > > thanks folks
