Re: [PATCH 0/2] drivers: android: binder: Introduce Cluster Aware Thread Selection

[Alice Ryhl]

On Wed, Jul 15, 2026 at 03:35:50AM +0900, trieu2.huynh wrote:
>   Motivation
>   ----------
> 
> On asymmetric multi-cluster ARM64 SoCs, the default binder thread
> selection is topology-blind. Cross-cluster thread wakeups incur severe
> cache-coherency overhead.
> 
> Measured performance test [1], especially with schd-dbg tiered threads [2]
> on baseline (10K iter, 16B payload):
> 
>   Class       Tier              Avg Latency    Count / % of txns
>   -----       ----              -----------    -----------------
>   SCHED_FIFO  Same-core         0.089 ms       9,963 / 99.6%
>   (max prio)  Same-cluster      0.120 ms          13 /  0.1%
>               Cross-cluster     0.140 ms          24 /  0.2%
>               -----------------------------------------------------
>   Normal      Same-core         0.130 ms       4,623 / 46.2%
>   (Other)     Same-cluster      0.140 ms       3,290 / 32.9%
>               Cross-cluster     0.190 ms       2,087 / 20.9%
> 
> Key Observations:
> (*) For SCHED_FIFO tasks, the scheduler aggressively locks the affinity,
>     keeping 99.6% of txns on the same core, establishing the hardware's
>     ideal latency ceiling (~0.089 ms).
> (*) For normal tasks, selection is highly fragmented (only 46.2% on
>     same-core). Cross-cluster transactions are ~46% slower (0.19 vs
>     0.13 ms) due to interconnect overhead and cache invalidation.
> (*) CTABS aims to close this gap for normal threads by enforcing affinity.

I've been told that GKI has patched wake_up_sync() to make it place the
recipient on the same CPU if nothing else is scheduled to run there.

* http://r.android.com/1362918
* http://r.android.com/1145589

Are these patches included in the tree from which you took this
benchmark?

Alice