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Thank you Mattias for the comments and question, please let me try to
explain the same below
We shouldn't have a separate CPU/cache hierarchy API instead?
Based on the intention to bring in CPU lcores which share same L3 (for
better cache hits and less noisy neighbor) current API focuses on using
Last Level Cache. But if the suggestion is `there are SoC where L2 cache
are also shared, and the new API should be provisioned`, I am also
comfortable with the thought.
Could potentially be built on the 'hwloc' library.
There are 3 reason on AMD SoC we did not explore this path, reasons are
1. depending n hwloc version and kernel version certain SoC hierarchies
are not available
2. CPU NUMA and IO (memory & PCIe) NUMA are independent on AMD Epyc Soc.
3. adds the extra dependency layer of library layer to be made available
to work.
hence we have tried to use Linux Documented generic layer of `sysfs CPU
cache`.
I will try to explore more on hwloc and check if other libraries within
DPDK leverages the same.
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.
yes, totally understand as some SoC, multiple lcores shares same L2 cache.
Can we rework the API to be rte_get_cache_<function> where user argument
is desired lcore index.
1. index-1: SMT threads
2. index-2: threads sharing same L2 cache
3. index-3: threads sharing same L3 cache
4. index-MAX: identify the threads sharing last level cache.
< 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.
While the MACRO are simple wrapper invoking appropriate API. can this be
worked out in this fashion?
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