[PATCH v7 1/7] eal: add static per-lcore memory allocation facility

[Mattias Rönnblom]

On 2024-10-10 00:15, Morten Brørup wrote:
>> From: Mattias Rönnblom [mailto:mattias.ronnblom at ericsson.com]
>> Sent: Wednesday, 18 September 2024 10.26
>>
>> Introduce DPDK per-lcore id variables, or lcore variables for short.
>>
>> An lcore variable has one value for every current and future lcore
>> id-equipped thread.
>>
>> The primary <rte_lcore_var.h> use case is for statically allocating
>> small, frequently-accessed data structures, for which one instance
>> should exist for each lcore.
>>
>> Lcore variables are similar to thread-local storage (TLS, e.g., C11
>> _Thread_local), but decoupling the values' life time with that of the
>> threads.
>>
>> Lcore variables are also similar in terms of functionality provided by
>> FreeBSD kernel's DPCPU_*() family of macros and the associated
>> build-time machinery. DPCPU uses linker scripts, which effectively
>> prevents the reuse of its, otherwise seemingly viable, approach.
>>
>> The currently-prevailing way to solve the same problem as lcore
>> variables is to keep a module's per-lcore data as RTE_MAX_LCORE-sized
>> array of cache-aligned, RTE_CACHE_GUARDed structs. The benefit of
>> lcore variables over this approach is that data related to the same
>> lcore now is close (spatially, in memory), rather than data used by
>> the same module, which in turn avoid excessive use of padding,
>> polluting caches with unused data.
>>
>> Signed-off-by: Mattias Rönnblom <mattias.ronnblom at ericsson.com>
>> Acked-by: Morten Brørup <mb at smartsharesystems.com>
> 
>> --- /dev/null
>> +++ b/lib/eal/common/eal_common_lcore_var.c
>> @@ -0,0 +1,79 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(c) 2024 Ericsson AB
>> + */
>> +
>> +#include <inttypes.h>
>> +#include <stdlib.h>
>> +
>> +#ifdef RTE_EXEC_ENV_WINDOWS
>> +#include <malloc.h>
>> +#endif
> 
>  From what I can read on the internet, max_align_t is missing in stddef.h in MSVC [1], so try adding this to fix the Windows CI compilation failure:
> 
> #ifdef RTE_TOOLCHAIN_MSVC
> #include <cstddef>
> #endif

Please excuse my MSVC ignorance, but will this work in C? Looks like C++.

> 
> [1]: https://learn.microsoft.com/en-ie/answers/questions/1726147/why-max-align-t-not-defined-in-stddef-h-in-windows
>