Messages in this thread | | | Date | Tue, 29 Mar 2022 15:50:48 -0400 | From | Phil Auld <> | Subject | Re: [PATCH] arch/arm64: Fix topology initialization for core scheduling |
| |
On Tue, Mar 29, 2022 at 08:55:08PM +0200 Dietmar Eggemann wrote: > On 29/03/2022 17:20, Phil Auld wrote: > > On Tue, Mar 29, 2022 at 04:02:22PM +0200 Dietmar Eggemann wrote: > >> On 22/03/2022 17:03, Phil Auld wrote: > > [...] > > >> I assume this is for a machine which relies on MPIDR-based setup > >> (package_id == -1)? I.e. it doesn't have proper ACPI/(DT) data for > >> topology setup. > > > > Yes, that's my understanding. No PPTT. > > > >> > >> Tried on a ThunderX2 by disabling parse_acpi_topology() but then I end > >> up with a machine w/o SMT, so `stress-ng --prctl N` doesn't show this issue. > >> > >> Which machine were you using? > > > > This instance is an HPE Apollo 70 set to smt-4. I believe it's ThunderX2 > > chips. > > > > ARM (CN9980-2200LG4077-Y21-G) > I'm using the same processor just with ACPI/PPTT. >
Maybe I'm misinformed about these systems having no PPTT...
I'm reclaiming the system. Is there a way I can tell from userspace?
> # sudo dmidecode -t 4 | grep "Part Number" > Part Number: CN9980-2200LG4077-21-Y-G > Part Number: CN9980-2200LG4077-21-Y-G > > # cat /sys/devices/system/cpu/cpu0/topology/thread_siblings > 0,32,64,96 > > # cat /sys/kernel/debug/sched/domains/cpu0/domain*/name > SMT > MC > NUMA > > But no matter whether I disable parse_acpi_topology() or just force > `cpu_topology[cpu].package_id = -1` in this function, I always end up with: > > # cat /sys/kernel/debug/sched/domains/cpu0/domain*/name > MC > NUMA > > # cat /sys/devices/system/cpu/cpu0/topology/thread_siblings_list > 0 > > so no SMT sched domain. The MPIDR-based topology fallback code in > store_cpu_topology() forces `cpuid_topo->thread_id = -1`.
Right. So since I'm getting SMT it must not have package_id == -1. In which case you should be able to reproduce it because it must be that the call the update_siblings_masks() is required. That appears to only be called from store_cpu_topology() which is after the scheduler has already setup the core pointers.
The fix could be the same but I should reword the commit message since it should effect all SMT arm systems I'd think.
Or maybe the ACPI topology code should call update_sibling_masks().
> > IMHO this is why on my machine I don't see this issue while running: > > root@oss-apollo7007:~# stress-ng --prctl 256 -t 60 > stress-ng: info: [2388042] dispatching hogs: 256 prctl > > Is there something I miss in my setup to provoke this issue? >
Make sure you have a stress-ng that is new enough and built against headers that have the CORE_SCHED prctls defined.
BTW, thanks for taking a look.
Cheers, Phil
> [...] >
--
| |