Re: [RFC 0/2] introduce LLC aware functions

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2024-08-27 17:10, Vipin Varghese wrote:
> As core density continues to increase, chiplet-based
> core packing has become a key trend. In AMD SoC EPYC
> architectures, core complexes within the same chiplet
> share a Last-Level Cache (LLC). By packing logical cores
> within the same LLC, we can enhance pipeline processing
> stages due to reduced latency and improved data locality.
> 
> To leverage these benefits, DPDK libraries and examples
> can utilize localized lcores. This approach ensures more
> consistent latencies by minimizing the dispersion of lcores
> across different chiplet complexes and enhances packet
> processing by ensuring that data for subsequent pipeline
> stages is likely to reside within the LLC.
> 

We shouldn't have a separate CPU/cache hierarchy API instead?

Could potentially be built on the 'hwloc' library.

I much agree cache/core topology may be of interest of the application 
(or a work scheduler, like a DPDK event device), but it's not limited to 
LLC. It may well be worthwhile to care about which cores shares L2 
cache, for example. Not sure the RTE_LCORE_FOREACH_* approach scales.

> < Function: Purpose >
> ---------------------
>   - rte_get_llc_first_lcores: Retrieves all the first lcores in the shared LLC.
>   - rte_get_llc_lcore: Retrieves all lcores that share the LLC.
>   - rte_get_llc_n_lcore: Retrieves the first n or skips the first n lcores in the shared LLC.
> 
> < MACRO: Purpose >
> ------------------
> RTE_LCORE_FOREACH_LLC_FIRST: iterates through all first lcore from each LLC.
> RTE_LCORE_FOREACH_LLC_FIRST_WORKER: iterates through all first worker lcore from each LLC.
> RTE_LCORE_FOREACH_LLC_WORKER: iterates lcores from LLC based on hint (lcore id).
> RTE_LCORE_FOREACH_LLC_SKIP_FIRST_WORKER: iterates lcores from LLC while skipping first worker.
> RTE_LCORE_FOREACH_LLC_FIRST_N_WORKER: iterates through `n` lcores from each LLC.
> RTE_LCORE_FOREACH_LLC_SKIP_N_WORKER: skip first `n` lcores, then iterates through reaming lcores in each LLC.
> 
> Vipin Varghese (2):
>    eal: add llc aware functions
>    eal/lcore: add llc aware for each macro
> 
>   lib/eal/common/eal_common_lcore.c | 279 ++++++++++++++++++++++++++++--
>   lib/eal/include/rte_lcore.h       |  89 ++++++++++
>   2 files changed, 356 insertions(+), 12 deletions(-)
>