Re: [RFC patch v3 00/20] Cache aware scheduling

[Shrikanth Hegde]

> tl;dr
>
> o Benchmark that prefer co-location and run in threaded mode see
>    a benefit including hackbench at high utilization and schbench
>    at low utilization.
>
> o schbench (both new and old but particularly the old) regresses
>    quite a bit on the tial latency metric when #workers cross the
>    LLC size.
>
> o client-server benchmarks where client and servers are threads
>    from different processes (netserver-netperf, tbench_srv-tbench,
>    services of DeathStarBench) seem to noticeably regress due to
>    lack of co-location between the communicating client and server.
>
>    Not sure if WF_SYNC can be an indicator to temporarily ignore
>    the preferred LLC hint.
>
> o stream regresses in some runs where the occupancy metrics trip
>    and assign a preferred LLC for all the stream threads bringing
>    down performance in !50% of the runs.

- When you have SMT systems, threads will go faster if they run in ST mode.
If aggregation happens in a LLC, they might end up with lower IPC.

> Full data from my testing is as follows:
>
> o Machine details
>
> - 3rd Generation EPYC System
> - 2 sockets each with 64C/128T
> - NPS1 (Each socket is a NUMA node)
> - C2 Disabled (POLL and C1(MWAIT) remained enabled)
>
> o Kernel details
>
> tip:      tip:sched/core at commit 914873bc7df9 ("Merge tag
>             'x86-build-2025-05-25' of
>             git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")
>
> llc-aware-lb-v3: tip + this series as is