linux-kernel - Re: [PATCH V2] arm64: add SCHED

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Date:   Tue, 26 Apr 2022 07:40:53 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     王擎 <wangqing@...o.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>
Subject: Re: [PATCH V2] arm64: add SCHED_CLUSTER's dependency on ACPI

On Tue, Apr 26, 2022 at 02:23:25AM +0000, 王擎 wrote:
> 
> >> 
> >> >> From: Wang Qing <wangqing@...o.com>
> >> >> 
> >> >> cluster sched_domain configured by cpu_topology[].cluster_sibling, 
> >> >> which is set by cluster_id, cluster_id can only get from ACPI.
> >> >> 
> >> >> If the system does not enable ACPI, cluster_id is always -1, even enable
> >> >> SCHED_CLUSTER is invalid, this is misleading. 
> >> >> 
> >> >> So we add SCHED_CLUSTER's dependency on ACPI here.
> >> >>
> >> >
> >> >Any reason why this can't be extended to support DT based systems via
> >> >cpu-map in the device tree. IMO we almost have everything w.r.t topology
> >> >in DT and no reason to deviate this feature between ACPI and DT.
> >> >
> >> That's the problem, we parse out "cluster" info according to the
> >> description in cpu-map, but do assign it to package_id, which used to
> >> configure the MC sched domain, not cluster sched domain.
> >>
> >
> >Right, we haven't updated the code after updating the bindings to match
> >ACPI sockets which are the physical package boundaries. Clusters are not
> >the physical boundaries and the current topology code is not 100% aligned
> >with the bindings after Commit 849b384f92bc ("Documentation: DT: arm: add
> >support for sockets defining package boundaries")
>
> I see, but this commit is a long time ago, why hasn't it been used widely.
> Maybe I can help about it if you need.
>

I assume no one cared or had a requirement for the same.

--
Regards,
Sudeep