| Message ID | YpZYPokZr9s4uwtt@p100 (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Drop CONFIG_SCHED_MC | expand |
On Tue, 31 May 2022, Helge Deller wrote: > Mikulas noticed that the parisc kernel crashes in sd_init() if > CONFIG_SCHED_MC is enabled. > Multicore-scheduling is probably not very useful on parisc, so simply > drop this option. > > Signed-off-by: Helge Deller <deller@gmx.de> > Noticed-by: Mikulas Patocka <mpatocka@redhat.com> > Cc: <stable@vger.kernel.org> # 5.18 Hi I think that we should fix the root cause instead of trying to treat the symptoms. Some more testing showed that: in sd_init: tl->mask(cpu) returns an empty mask tl->mask is cpu_coregroup_mask in cpu_coregroup_mask: cpu_topology[cpu].core_sibling is an empty mask, that gets returned to sd_init In arch/parisc/kernel/topology.c: init_cpu_topology is called before store_cpu_topology, but it depends on the variable dualcores_found being set by store_cpu_topology. Thus, it is not set. store_cpu_topology returns if cpuid_topo->core_id != -1, but during boot, store_cpu_topology is called before reset_cpu_topology, thus the member "core_id" is uninitialized zero and store_cpu_tolopogy does nothing. If these issues are addrssed, multicore scheduling will work. Mikulas
On Wed, 1 Jun 2022, Mikulas Patocka wrote: > > > On Tue, 31 May 2022, Helge Deller wrote: > > > Mikulas noticed that the parisc kernel crashes in sd_init() if > > CONFIG_SCHED_MC is enabled. > > Multicore-scheduling is probably not very useful on parisc, so simply > > drop this option. > > > > Signed-off-by: Helge Deller <deller@gmx.de> > > Noticed-by: Mikulas Patocka <mpatocka@redhat.com> > > Cc: <stable@vger.kernel.org> # 5.18 > > Hi > > I think that we should fix the root cause instead of trying to treat the > symptoms. > > Some more testing showed that: > > in sd_init: tl->mask(cpu) returns an empty mask > tl->mask is cpu_coregroup_mask > in cpu_coregroup_mask: cpu_topology[cpu].core_sibling is an empty mask, > that gets returned to sd_init > > In arch/parisc/kernel/topology.c: > init_cpu_topology is called before store_cpu_topology, but it depends on > the variable dualcores_found being set by store_cpu_topology. Thus, it is > not set. > > store_cpu_topology returns if cpuid_topo->core_id != -1, but during boot, > store_cpu_topology is called before reset_cpu_topology, thus the member > "core_id" is uninitialized zero and store_cpu_tolopogy does nothing. > > If these issues are addrssed, multicore scheduling will work. I've found that this fixes it. Mikulas --- arch/parisc/kernel/topology.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Index: linux-2.6/arch/parisc/kernel/topology.c =================================================================== --- linux-2.6.orig/arch/parisc/kernel/topology.c 2022-06-01 15:32:59.000000000 +0200 +++ linux-2.6/arch/parisc/kernel/topology.c 2022-06-01 16:47:36.000000000 +0200 @@ -95,7 +95,8 @@ static struct sched_domain_topology_leve */ void __init init_cpu_topology(void) { + reset_cpu_topology(); /* Set scheduler topology descriptor */ - if (dualcores_found) + /*if (dualcores_found)*/ set_sched_topology(parisc_mc_topology); }
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig index bd22578859d0..34591a981cb7 100644 --- a/arch/parisc/Kconfig +++ b/arch/parisc/Kconfig @@ -281,14 +281,6 @@ config SMP If you don't know what to do here, say N. -config SCHED_MC - bool "Multi-core scheduler support" - depends on GENERIC_ARCH_TOPOLOGY && PA8X00 - help - Multi-core scheduler support improves the CPU scheduler's decision - making when dealing with multi-core CPU chips at a cost of slightly - increased overhead in some places. If unsure say N here. - config IRQSTACKS bool "Use separate kernel stacks when processing interrupts" default y diff --git a/arch/parisc/kernel/topology.c b/arch/parisc/kernel/topology.c index 9696e3cb6a2a..71a678ceb33a 100644 --- a/arch/parisc/kernel/topology.c +++ b/arch/parisc/kernel/topology.c @@ -81,10 +81,6 @@ void store_cpu_topology(unsigned int cpuid) } static struct sched_domain_topology_level parisc_mc_topology[] = { -#ifdef CONFIG_SCHED_MC - { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) }, -#endif - { cpu_cpu_mask, SD_INIT_NAME(DIE) }, { NULL, }, };
Mikulas noticed that the parisc kernel crashes in sd_init() if CONFIG_SCHED_MC is enabled. Multicore-scheduling is probably not very useful on parisc, so simply drop this option. Signed-off-by: Helge Deller <deller@gmx.de> Noticed-by: Mikulas Patocka <mpatocka@redhat.com> Cc: <stable@vger.kernel.org> # 5.18