Re: [PATCH] PM: QoS: Add support for CPU affinity mask-based CPUs latency QoS

[Zhongqiu Han]

On 4/24/2025 6:25 PM, Christian Loehle wrote:
> On 4/24/25 10:52, Zhongqiu Han wrote:
> > Currently, the PM QoS framework supports global CPU latency QoS and
> > per-device CPU latency QoS requests. An example of using global CPU
> > latency QoS is a commit 2777e73fc154 ("scsi: ufs: core: Add CPU latency
> > QoS support for UFS driver") that improved random io performance by 15%
> > for ufs on specific device platform.
> >
> > However, this prevents all CPUs in the system from entering C states.
> > Typically, some threads or drivers know which specific CPUs they are
> > interested in. For example, drivers with IRQ affinity only want interrupts
> > to wake up and be handled on specific CPUs. Similarly, kernel thread bound
> > to specific CPUs through affinity only care about the latency of those
> > particular CPUs.
> >
> > This patch introduces support for partial CPUs PM QoS using a CPU affinity
> > mask, allowing flexible and more precise latency QoS settings for specific
> > CPUs. This can help save power, especially on heterogeneous platforms with
> > big and little cores, as well as some power-conscious embedded systems for
> > example:
> >
> >                    driver A       rt kthread B      module C
> > QoS cpu mask:       0-3              2-5              6-7
> > target latency:     20               30               50
> >                      |                |                |
> >                      v                v                v
> >                      +---------------------------------+
> >                      |        PM  QoS  Framework       |
> >                      +---------------------------------+
> >                      |                |                |
> >                      v                v                v
> > cpu mask:          0-3            2-3,4-5            6-7
> > actual latency:    20             20, 30             50
> >
> > Implement this support based on per-device CPU latency PM QoS.
> >
> > Signed-off-by: Zhongqiu Han <quic_zhonhan@xxxxxxxxxxx>
>
> I like the idea!
> The interface does need an in-tree user, why not convert the UFS driver?

Thanks Christian for the review.

As far as I know, the UFS IRQ affinity varies across different
platforms, so a universal solution is needed (we need to investigate
whether there is already a solution or add parameters like intr_mask to
represent the IRQ affinity mask). Let me investigate it, or raise other
user patches as a patch series in PATCH v2 as soon as possible. Thanks


--
Thx and BRs,
Zhongqiu Han