[PATCH V2] arm64: add SCHED_CLUSTER's dependency on ACPI

[王擎]

>> 
>>>> On Tue, Apr 26, 2022 at 06:52:34AM +0000, 王擎 wrote:
>>>>>
>>>>>>>>>>> From: Wang Qing <wangqing@xxxxxxxx>
>
>[...]
>
>>>      .---------------.
>>> CPU   |0 1 2 3 4 5 6 7|
>>>      +---------------+
>>> uarch |l l l l m m m b| (so called tri-gear: little, medium, big)
>>>      +---------------+
>>>  L2  |   |   | | | | |
>>>      +---------------+
>>>  L3  |<--         -->|
>>>      +---------------+
>>>      |<-- cluster -->|
>>>      +---------------+
>>>      |<--   DSU   -->|
>>>      '---------------'
>>>
>>> (and I'm not saying here it does!) then the existing SCHED_CLUSTER
>>> should be used in DT as well. Since it provides exactly the same
>>> functionality for the task scheduler no matter whether it's setup from
>>> ACPI or DT.
>>>
>>> parse_cluster() -> parse_core() should be changed to be able to decode
>>> both id's (package_id and cluster_id) in this case.
>> 
>> Totally agree, but not implemented yet. Because now cluster_id is used
>> to describe the package/socket, the modification will involve all DTS.
>
>You're talking about the fact that 1. level clusterX (1) in cpu_map is
>used to set `cpu_topology[cpu].package_id`, right? That's the
>information for the DIE layer.
>The first level cluster[0,1,2] spawn all 8 CPUs and form 3 groups of
>CPUS (0-3, 4-6, 7), the later sched groups of the DIE sched domain.
>We don't have any socketN since it is a single socket system. Think
>about a system with 2 DSUs where you would have socket[0,1].
>
>Sub-chapter 4 in `Documentation/devicetree/bindings/cpu/cpu-topology.txt`:
>
>cpu-map {
>        socket0 {
>                cluster0 { <--- (1)
>
>Sub-chapter 3 says:
>
>  - cluster node
>
>    ... A system can contain several layers of clustering within a   
>    single physical socket and cluster nodes can be contained in parent 
>    cluster nodes.
>
>    A cluster node's child nodes must be:
>      one or more cluster nodes
>
>This multi-level cluster thing hasn't been coded yet.
>
>parse_cluster()
>
>    ...
>    /*
>     * First check for child clusters; we currently ignore any
>     * information about the nesting of clusters and present the
>     * scheduler with a flat list of them.
>     */
>    ...
>
>[...]
>
>>> I pimped my Hikey 960 to look like one of those Armv9 4-3-1 systems with
>>> L2-complexes on the LITTLES and I get:
>> 
>> This system is exactly what I mentioned, but I have a question,
>> How did you parse out the cluster_id based on foo0/foo2?
>> Because if ACPI is not used, cluster_id is always -1.
>
>I haven't put in the extension to decode a 2-level clusterX cpu_map in
>parse_cluster() -> parse_core(). I just did a mock-up for illustration
>purpose inside parse_core() for my H960 with a 4-3-1 cpu-map:
>
>cpu-map
>    cluster0
>        core0
>        core1
>        core2
>        core3
>    cluster1
>        core0
>        core1
>        core2
>    cluster2
>        core0
>
>diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
>index 1d6636ebaac5..8af40f13fdb5 100644
>--- a/drivers/base/arch_topology.c
>+++ b/drivers/base/arch_topology.c
>@@ -529,6 +529,11 @@ static int __init parse_core(struct device_node *core, int package_id,
> 
>                cpu_topology[cpu].package_id = package_id;
>                cpu_topology[cpu].core_id = core_id;
>+
>+               /* mock-up CLS SD on 4-3-1 Armv9 DSU cluster w/ L2-complexes */
>+               if (cpu <= 3)
>+                       cpu_topology[cpu].cluster_id = cpu / 2;
>+
>        } else if (leaf && cpu != -ENODEV) {
>                pr_err("%pOF: Can't get CPU for leaf core\n", core);
>                return -EINVAL;
>
>And on the scheduler-side I only had to enable CONFIG_SCHED_CLUSTER and
>everything worked just fine, no need for any arm64-specific topo table
>and alike.
>
>IMHO, this is what you have to do. Make a 2 level cluster cpumap:
>
>cpu-map
>    cluster0
>        cluster0
>            core0
>            core1
>        cluster1
>            core2
>            core3
>    cluster1
>        core0
>        core1
>        core2
>    cluster2
>        core0
>
>parse-able and set `cpu_topology[cpu].cluster_id` in parse_core().

Oh, there are many ways I can implement it in my own system, but my
purpose here is to modify the mainline code so that all Android
developers can use it.

> 
>> What I want to do is to change the foo0/foo2 to complex0/complex2 here,
>> then parse it like parse_cluster() -> parse_complex() -> parse_core().
>
>You should read `Documentation/devicetree/bindings/cpu/cpu-topology.txt`
>and implement the multi-level cluster approach instead. Big advantage
>would be that there won't be any DT related changes/extensions needed.
>

Thanks for the advice, I will consider about it.
Qing

>[...]
>
>> Yes, that's what I want, but still a little confused, why we use MC to
>> describe "cluster" and use CLS describe "complex", can you show some details?
>
>The DT entity `cluster` has nothing to do with the task scheduler domain
>name `SCHED_CLUSTER`. The name is actually meaningless and just there for
>debug purposes.