Hello Mete, On 10/7/2026 3:49 PM, Mete Durlu wrote: > On 01/10/2026 21:28, K Prateek Nayak wrote: >> When the topology mode is TOPOLOGY_MODE_HW, topology_init_early() >> already parses the set of socket present on the system. >> >> Use the socket_info to configure the sparsebitmask (sbm) properties for >> the system - namely the number of sockets and maximum threads in a >> socket instance. >> >> arch_sbm_cpu_instance_id() traverses all socket instances to find >> a matching CPU which is not optimal but instance ID is only checked >> when the CPU is coming online. Since this is a rare event, the >> inefficiency is tolerable. >> >> Signed-off-by: K Prateek Nayak <[email protected]> >> --- >> Build tested with LKP's s390 randconfig with QEMU cmdline: >> >> qemu-system-s390x \ >> -cpu max \ >> -smp 2 \ >> -m 2048 \ >> -kernel ./arch/s390/boot/vmlinux \ >> -append "console=ttyAMA0 earlycon ignore_loglevel log_buf_len=10M >> print_fatal_signals=1 LOGLEVEL=8 sched_debug" \ >> -nographic >> >> Note: Since ctop needs KVM acceleration to emulate TOPOLOGY_MODE_HW, the >> actual spasemask setting is only build tested at the moment. >> >> XXX: Any way around this using cross-compile and QEMU? >> --- >> arch/s390/kernel/topology.c | 52 +++++++++++++++++++++++++++++++++++++ >> 1 file changed, 52 insertions(+) >> >> diff --git a/arch/s390/kernel/topology.c b/arch/s390/kernel/topology.c >> index 1377c6f3f670..80dc51f5ce6f 100644 >> --- a/arch/s390/kernel/topology.c >> +++ b/arch/s390/kernel/topology.c >> @@ -20,6 +20,7 @@ >> #include <linux/init.h> >> #include <linux/slab.h> >> #include <linux/cpu.h> >> +#include <linux/sbm.h> >> #include <linux/smp.h> >> #include <linux/mm.h> >> #include <linux/nodemask.h> >> @@ -561,6 +562,55 @@ static int __init detect_polarization(union >> topology_entry *tle) >> return tl_core->pp != POLARIZATION_HRZ; >> } > > topology_init_early() is called once during early boot and never again. > Considering that s390's topology can change during runtime this > implementation won't work as sbm won't be able to adapt. > On s390 max_threads_per_instance can change during runtime. > > Like sashiko pointed out, this approach also does not consider > any newly added cpus. > > IMHO, there is a slight redesign required so that smb_set_topology() > and smb_init() can be called each time a topology rebuild is necessary.
So based on my limited understanding, doesn't store_topology() populate the mask for the entire system on s390? Are you saying that can change or that stsi() may return a partial topology for only the online CPUs? Since s390 default enables hotplug, I couldn't easily grep the hotplug bits so please forgive if I missed something. -- Thanks and Regards, Prateek
