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

[Trieu Huynh]

On Wed, Jul 15, 2026 at 09:17:48AM +0000, Alice Ryhl wrote:
> 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?
I am currently using QC source which is based on GKI 6.1.145 [1]
AFAICS, they've already been included while I'm doing this work:
(*) kernel/common: android14-6.1 [2]
https://android.googlesource.com/kernel/common/+/06dc94f19d2f5426a9ab761512b61c0c07c9d750
https://android.googlesource.com/kernel/common/+/3a9495889492ae5132ea995723bf5ed6b045d8fa
(*) kernel/qcom: kernel.lnx.6.1.r31-rel [3]
https://git.codelinaro.org/clo/la/kernel/qcom/-/commit/3a9495889492ae5132ea995723bf5ed6b045d8fa
https://git.codelinaro.org/clo/la/kernel/qcom/-/commit/06dc94f19d2f5426a9ab761512b61c0c07c9d750

[1] https://source.android.com/docs/core/architecture/kernel/gki-android14-6_1-release-builds?hl=vi#september-2025-releases_1
[2] https://android.googlesource.com/kernel/common/+/refs/heads/android14-6.1
[3] https://git.codelinaro.org/clo/la/kernel/qcom/-/tree/kernel.lnx.6.1.r31-rel

BRs,
> 
> Alice