Hi Darren,
On 2022/4/12 4:53, Darren Hart wrote:
Ampere Altra defines CPU clusters in the ACPI PPTT. They share a Snoop Control Unit, but have no shared CPU-side last level cache.
cpu_coregroup_mask() will return a cpumask with weight 1, while cpu_clustergroup_mask() will return a cpumask with weight 2.
As a result, build_sched_domain() will BUG() once per CPU with:
BUG: arch topology borken the CLS domain not a subset of the MC domain
The MC level cpumask is then extended to that of the CLS child, and is later removed entirely as redundant. This sched domain topology is an improvement over previous topologies, or those built without SCHED_CLUSTER, particularly for certain latency sensitive workloads. With the current scheduler model and heuristics, this is a desirable default topology for Ampere Altra and Altra Max system.
Rather than create a custom sched domains topology structure and introduce new logic in arch/arm64 to detect these systems, update the core_mask so coregroup is never a subset of clustergroup, extending it to cluster_siblings if necessary. Only do this if CONFIG_SCHED_CLUSTER is enabled to avoid also changing the topology (MC) when CONFIG_SCHED_CLUSTER is disabled.
This has the added benefit over a custom topology of working for both symmetric and asymmetric topologies. It does not address systems where the CLUSTER topology is above a populated MC topology, but these are not considered today and can be addressed separately if and when they appear.
The final sched domain topology for a 2 socket Ampere Altra system is unchanged with or without CONFIG_SCHED_CLUSTER, and the BUG is avoided:
For CPU0:
CONFIG_SCHED_CLUSTER=y CLS [0-1] DIE [0-79] NUMA [0-159]
CONFIG_SCHED_CLUSTER is not set DIE [0-79] NUMA [0-159]
Signed-off-by: Darren Hart darren@os.amperecomputing.com Suggested-by: Barry Song song.bao.hua@hisilicon.com Reviewed-by: Barry Song song.bao.hua@hisilicon.com Acked-by: Sudeep Holla sudeep.holla@arm.com Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: "Rafael J. Wysocki" rafael@kernel.org Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Vincent Guittot vincent.guittot@linaro.org Cc: D. Scott Phillips scott@os.amperecomputing.com Cc: Ilkka Koskinen ilkka@os.amperecomputing.com Cc: stable@vger.kernel.org # 5.16.x
v1: Drop MC level if coregroup weight == 1 v2: New sd topo in arch/arm64/kernel/smp.c v3: No new topo, extend core_mask to cluster_siblings v4: Rebase on 5.18-rc1 for GregKH to pull. Add IS_ENABLED(CONFIG_SCHED_CLUSTER). v5: Rebase on 5.18-rc2 for GregKH to pull. Add collected tags. No other changes.
drivers/base/arch_topology.c | 9 +++++++++ 1 file changed, 9 insertions(+)
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.
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:
[ 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 [ 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