Re: [PATCH v2 0/5] PM QoS: Add CPU affinity latency QoS support and resctrl integration

[Christian Loehle <christian.loehle@arm.com>]

On 7/21/25 13:40, Zhongqiu Han wrote:
> Hi all,
> 
> This patch series introduces support for CPU affinity-based latency
> constraints in the PM QoS framework. The motivation is to allow
> finer-grained power management by enabling latency QoS requests to target
> specific CPUs, rather than applying system-wide constraints.
> 
> The current PM QoS framework supports global and per-device CPU latency
> constraints. However, in many real-world scenarios, such as IRQ affinity
> or CPU-bound kernel threads, only a subset of CPUs are
> performance-critical. Applying global constraints in such cases
> unnecessarily prevents other CPUs from entering deeper C-states, leading
> to increased power consumption.
> 
> This series addresses that limitation by introducing a new interface that
> allows latency constraints to be applied to a CPU mask. This is
> particularly useful on heterogeneous platforms (e.g., big.LITTLE) and
> embedded systems where power efficiency is critical for example:
> 
>                         driver A       rt kthread B      module C
>   CPU IDs (mask):         0-3              2-5              6-7
>   target latency(us):     20               30               100
>                           |                |                |
>                           v                v                v
>                           +---------------------------------+
>                           |        PM  QoS  Framework       |
>                           +---------------------------------+
>                           |                |                |
>                           v                v                v
>   CPU IDs (mask):        0-3            2-3,4-5            6-7
>   runtime latency(us):   20             20, 30             100
> 
> The current implementation includes only cpu_affinity_latency_qos_add()
> and cpu_affinity_latency_qos_remove() interfaces. An update interface is
> planned for future submission, along with PM QoS optimizations in the UFS
> subsystem.

So what's needed for the UFS use-case additionally?
Would adding that here be too much?