Re: [PATCH v5] topology: make core_mask include at least cluster_siblings

[Darren Hart <darren@os.amperecomputing.com>]

On Thu, Sep 15, 2022 at 08:01:18PM +0800, Yicong Yang wrote:
> Hi Darren,
> 

Hi Yicong,

...

> > diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> > index 1d6636ebaac5..5497c5ab7318 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -667,6 +667,15 @@ const struct cpumask *cpu_coregroup_mask(int cpu)
> >  			core_mask = &cpu_topology[cpu].llc_sibling;
> >  	}
> >  
> > +	/*
> > +	 * For systems with no shared cpu-side LLC but with clusters defined,
> > +	 * extend core_mask to cluster_siblings. The sched domain builder will
> > +	 * then remove MC as redundant with CLS if SCHED_CLUSTER is enabled.
> > +	 */
> > +	if (IS_ENABLED(CONFIG_SCHED_CLUSTER) &&
> > +	    cpumask_subset(core_mask, &cpu_topology[cpu].cluster_sibling))
> > +		core_mask = &cpu_topology[cpu].cluster_sibling;
> > +
> >  	return core_mask;
> >  }
> >  
> 
> Is this patch still necessary for Ampere after Ionela's patch [1], which
> will limit the cluster's span within coregroup's span.

Yes, see:
https://lore.kernel.org/lkml/YshYAyEWhE4z%2FKpB@fedora/

Both patches work together to accomplish the desired sched domains for the
Ampere Altra family.

> 
> I found an issue that the NUMA domains are not built on qemu with:
> 
> qemu-system-aarch64 \
>         -kernel ${Image} \
>         -smp 8 \
>         -cpu cortex-a72 \
>         -m 32G \
>         -object memory-backend-ram,id=node0,size=8G \
>         -object memory-backend-ram,id=node1,size=8G \
>         -object memory-backend-ram,id=node2,size=8G \
>         -object memory-backend-ram,id=node3,size=8G \
>         -numa node,memdev=node0,cpus=0-1,nodeid=0 \
>         -numa node,memdev=node1,cpus=2-3,nodeid=1 \
>         -numa node,memdev=node2,cpus=4-5,nodeid=2 \
>         -numa node,memdev=node3,cpus=6-7,nodeid=3 \
>         -numa dist,src=0,dst=1,val=12 \
>         -numa dist,src=0,dst=2,val=20 \
>         -numa dist,src=0,dst=3,val=22 \
>         -numa dist,src=1,dst=2,val=22 \
>         -numa dist,src=1,dst=3,val=24 \
>         -numa dist,src=2,dst=3,val=12 \
>         -machine virt,iommu=smmuv3 \
>         -net none \
>         -initrd ${Rootfs} \
>         -nographic \
>         -bios QEMU_EFI.fd \
>         -append "rdinit=/init console=ttyAMA0 earlycon=pl011,0x9000000 sched_verbose loglevel=8"
> 
> I can see the schedule domain build stops at MC level since we reach all the
> cpus in the system:
> 
> [    2.141316] CPU0 attaching sched-domain(s):
> [    2.142558]  domain-0: span=0-7 level=MC
> [    2.145364]   groups: 0:{ span=0 cap=964 }, 1:{ span=1 cap=914 }, 2:{ span=2 cap=921 }, 3:{ span=3 cap=964 }, 4:{ span=4 cap=925 }, 5:{ span=5 cap=964 }, 6:{ span=6 cap=967 }, 7:{ span=7 cap=967 }
> [    2.158357] CPU1 attaching sched-domain(s):
> [    2.158964]  domain-0: span=0-7 level=MC
> [...]
> 
> Without this the NUMA domains are built correctly:
> 

Without which? My patch, Ionela's patch, or both?

> [    2.008885] CPU0 attaching sched-domain(s):
> [    2.009764]  domain-0: span=0-1 level=MC
> [    2.012654]   groups: 0:{ span=0 cap=962 }, 1:{ span=1 cap=925 }
> [    2.016532]   domain-1: span=0-3 level=NUMA
> [    2.017444]    groups: 0:{ span=0-1 cap=1887 }, 2:{ span=2-3 cap=1871 }
> [    2.019354]    domain-2: span=0-5 level=NUMA

I'm not following this topology - what in the description above should result in
a domain with span=0-5?


> [    2.019983]     groups: 0:{ span=0-3 cap=3758 }, 4:{ span=4-5 cap=1935 }
> [    2.021527]     domain-3: span=0-7 level=NUMA
> [    2.022516]      groups: 0:{ span=0-5 mask=0-1 cap=5693 }, 6:{ span=4-7 mask=6-7 cap=3978 }
> [...]
> 
> Hope to see your comments since I have no Ampere machine and I don't know
> how to emulate its topology on qemu.
> 
> [1] bfcc4397435d ("arch_topology: Limit span of cpu_clustergroup_mask()")
> 
> Thanks,
> Yicong

Thanks,

-- 
Darren Hart
Ampere Computing / OS and Kernel

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