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SubjectRe: [PATCH] arch_topology: Limit threads to one specific cluster
On Tue, May 24, 2022 at 05:05:22PM +0800, Gavin Shan wrote:
> Hi Sudeep,
>
> On 5/24/22 4:51 PM, Sudeep Holla wrote:
> > On Tue, May 24, 2022 at 04:12:12PM +0800, Gavin Shan wrote:
> > > The sibling information for one particular CPU is updated after ACPI
> > > PPTT table is parsed. struct cpu_topology::thread_sibling tracks the
> > > the CPUs in same core. However, cluster isn't considered when it's
> > > populated. In this case, multiple threads belonging to different
> > > clusters can be put together through the sibling information. It
> > > eventually leads to unexpected warning from sched subsystem.
> > >
> > > For example, the following warning is observed in a VM where we have
> > > 2 sockets, 4 clusters, 8 cores and 16 threads and the CPU topology
> > > is populated as below.
> > >
> > > CPU Socket-ID Cluster-ID Core-ID Thread-ID
> > > ----------------------------------------------
> > > 0 0 0 0 0
> > > 1 0 0 0 1
> > > 2 0 0 1 0
> > > 3 0 0 1 1
> > > 4 0 1 0 0
> > > 5 0 1 0 1
> > > 6 0 1 1 0
> > > 7 0 1 1 1
> > > 8 1 0 0 0
> > > 9 1 0 0 1
> > > 10 1 0 1 0
> > > 11 1 0 1 1
> > > 12 1 1 0 0
> > > 13 1 1 0 1
> > > 14 1 1 1 0
> > > 15 1 1 1 1
> > >
> > > [ 0.592181] CPU: All CPU(s) started at EL1
> > > [ 0.593766] alternatives: patching kernel code
> > > [ 0.595890] BUG: arch topology borken
> > > [ 0.597210] the SMT domain not a subset of the CLS domain
> > > [ 0.599286] child=0-1,4-5 sd=0-3
> > >
> > > # cat /sys/devices/system/cpu/cpu0/topology/cluster_cpus_list
> > > 0-3
> > > # cat /sys/devices/system/cpu/cpu0/topology/thread_siblings_list
> > > 0-1,4-5
> > >
> > > This fixes the issue by limiting threads to one specific cluster.
> > > With this applied, the unexpected warning disappears in the VM.
> > >
> >
> > I have similar fix but as part of bigger series[1] to get DT support in
> > line with ACPI.
> >
>
> Your patch resolves the issue I have. So please ignore mine. Sorry

Thanks for that.

> for the noise.
>

No worries, definitely not noise.

--
Regards,
Sudeep

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