4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Srikar Dronamraju srikar@linux.vnet.ibm.com
[ Upstream commit 2ea62630681027c455117aa471ea3ab8bb099ead ]
On a shared LPAR, Phyp will not update the CPU associativity at boot time. Just after the boot system does recognize itself as a shared LPAR and trigger a request for correct CPU associativity. But by then the scheduler would have already created/destroyed its sched domains.
This causes - Broken load balance across Nodes causing islands of cores. - Performance degradation esp if the system is lightly loaded - dmesg to wrongly report all CPUs to be in Node 0. - Messages in dmesg saying borken topology. - With commit 051f3ca02e46 ("sched/topology: Introduce NUMA identity node sched domain"), can cause rcu stalls at boot up.
The sched_domains_numa_masks table which is used to generate cpumasks is only created at boot time just before creating sched domains and never updated. Hence, its better to get the topology correct before the sched domains are created.
For example on 64 core Power 8 shared LPAR, dmesg reports
Brought up 512 CPUs Node 0 CPUs: 0-511 Node 1 CPUs: Node 2 CPUs: Node 3 CPUs: Node 4 CPUs: Node 5 CPUs: Node 6 CPUs: Node 7 CPUs: Node 8 CPUs: Node 9 CPUs: Node 10 CPUs: Node 11 CPUs: ... BUG: arch topology borken the DIE domain not a subset of the NUMA domain BUG: arch topology borken the DIE domain not a subset of the NUMA domain
numactl/lscpu output will still be correct with cores spreading across all nodes:
Socket(s): 64 NUMA node(s): 12 Model: 2.0 (pvr 004d 0200) Model name: POWER8 (architected), altivec supported Hypervisor vendor: pHyp Virtualization type: para L1d cache: 64K L1i cache: 32K NUMA node0 CPU(s): 0-7,32-39,64-71,96-103,176-183,272-279,368-375,464-471 NUMA node1 CPU(s): 8-15,40-47,72-79,104-111,184-191,280-287,376-383,472-479 NUMA node2 CPU(s): 16-23,48-55,80-87,112-119,192-199,288-295,384-391,480-487 NUMA node3 CPU(s): 24-31,56-63,88-95,120-127,200-207,296-303,392-399,488-495 NUMA node4 CPU(s): 208-215,304-311,400-407,496-503 NUMA node5 CPU(s): 168-175,264-271,360-367,456-463 NUMA node6 CPU(s): 128-135,224-231,320-327,416-423 NUMA node7 CPU(s): 136-143,232-239,328-335,424-431 NUMA node8 CPU(s): 216-223,312-319,408-415,504-511 NUMA node9 CPU(s): 144-151,240-247,336-343,432-439 NUMA node10 CPU(s): 152-159,248-255,344-351,440-447 NUMA node11 CPU(s): 160-167,256-263,352-359,448-455
Currently on this LPAR, the scheduler detects 2 levels of Numa and created numa sched domains for all CPUs, but it finds a single DIE domain consisting of all CPUs. Hence it deletes all numa sched domains.
To address this, detect the shared processor and update topology soon after CPUs are setup so that correct topology is updated just before scheduler creates sched domain.
With the fix, dmesg reports:
numa: Node 0 CPUs: 0-7 32-39 64-71 96-103 176-183 272-279 368-375 464-471 numa: Node 1 CPUs: 8-15 40-47 72-79 104-111 184-191 280-287 376-383 472-479 numa: Node 2 CPUs: 16-23 48-55 80-87 112-119 192-199 288-295 384-391 480-487 numa: Node 3 CPUs: 24-31 56-63 88-95 120-127 200-207 296-303 392-399 488-495 numa: Node 4 CPUs: 208-215 304-311 400-407 496-503 numa: Node 5 CPUs: 168-175 264-271 360-367 456-463 numa: Node 6 CPUs: 128-135 224-231 320-327 416-423 numa: Node 7 CPUs: 136-143 232-239 328-335 424-431 numa: Node 8 CPUs: 216-223 312-319 408-415 504-511 numa: Node 9 CPUs: 144-151 240-247 336-343 432-439 numa: Node 10 CPUs: 152-159 248-255 344-351 440-447 numa: Node 11 CPUs: 160-167 256-263 352-359 448-455
and lscpu also reports:
Socket(s): 64 NUMA node(s): 12 Model: 2.0 (pvr 004d 0200) Model name: POWER8 (architected), altivec supported Hypervisor vendor: pHyp Virtualization type: para L1d cache: 64K L1i cache: 32K NUMA node0 CPU(s): 0-7,32-39,64-71,96-103,176-183,272-279,368-375,464-471 NUMA node1 CPU(s): 8-15,40-47,72-79,104-111,184-191,280-287,376-383,472-479 NUMA node2 CPU(s): 16-23,48-55,80-87,112-119,192-199,288-295,384-391,480-487 NUMA node3 CPU(s): 24-31,56-63,88-95,120-127,200-207,296-303,392-399,488-495 NUMA node4 CPU(s): 208-215,304-311,400-407,496-503 NUMA node5 CPU(s): 168-175,264-271,360-367,456-463 NUMA node6 CPU(s): 128-135,224-231,320-327,416-423 NUMA node7 CPU(s): 136-143,232-239,328-335,424-431 NUMA node8 CPU(s): 216-223,312-319,408-415,504-511 NUMA node9 CPU(s): 144-151,240-247,336-343,432-439 NUMA node10 CPU(s): 152-159,248-255,344-351,440-447 NUMA node11 CPU(s): 160-167,256-263,352-359,448-455
Reported-by: Manjunatha H R manjuhr1@in.ibm.com Signed-off-by: Srikar Dronamraju srikar@linux.vnet.ibm.com [mpe: Trim / format change log] Tested-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/include/asm/topology.h | 5 +++++ arch/powerpc/kernel/smp.c | 5 +++++ arch/powerpc/mm/numa.c | 20 ++++++++++---------- 3 files changed, 20 insertions(+), 10 deletions(-)
--- a/arch/powerpc/include/asm/topology.h +++ b/arch/powerpc/include/asm/topology.h @@ -92,6 +92,7 @@ extern int stop_topology_update(void); extern int prrn_is_enabled(void); extern int find_and_online_cpu_nid(int cpu); extern int timed_topology_update(int nsecs); +extern void __init shared_proc_topology_init(void); #else static inline int start_topology_update(void) { @@ -113,6 +114,10 @@ static inline int timed_topology_update( { return 0; } + +#ifdef CONFIG_SMP +static inline void shared_proc_topology_init(void) {} +#endif #endif /* CONFIG_NUMA && CONFIG_PPC_SPLPAR */
#include <asm-generic/topology.h> --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -1156,6 +1156,11 @@ void __init smp_cpus_done(unsigned int m if (smp_ops && smp_ops->bringup_done) smp_ops->bringup_done();
+ /* + * On a shared LPAR, associativity needs to be requested. + * Hence, get numa topology before dumping cpu topology + */ + shared_proc_topology_init(); dump_numa_cpu_topology();
/* --- a/arch/powerpc/mm/numa.c +++ b/arch/powerpc/mm/numa.c @@ -1078,7 +1078,6 @@ static int prrn_enabled; static void reset_topology_timer(void); static int topology_timer_secs = 1; static int topology_inited; -static int topology_update_needed;
/* * Change polling interval for associativity changes. @@ -1306,11 +1305,8 @@ int numa_update_cpu_topology(bool cpus_l struct device *dev; int weight, new_nid, i = 0;
- if (!prrn_enabled && !vphn_enabled) { - if (!topology_inited) - topology_update_needed = 1; + if (!prrn_enabled && !vphn_enabled && topology_inited) return 0; - }
weight = cpumask_weight(&cpu_associativity_changes_mask); if (!weight) @@ -1423,7 +1419,6 @@ int numa_update_cpu_topology(bool cpus_l
out: kfree(updates); - topology_update_needed = 0; return changed; }
@@ -1551,6 +1546,15 @@ int prrn_is_enabled(void) return prrn_enabled; }
+void __init shared_proc_topology_init(void) +{ + if (lppaca_shared_proc(get_lppaca())) { + bitmap_fill(cpumask_bits(&cpu_associativity_changes_mask), + nr_cpumask_bits); + numa_update_cpu_topology(false); + } +} + static int topology_read(struct seq_file *file, void *v) { if (vphn_enabled || prrn_enabled) @@ -1608,10 +1612,6 @@ static int topology_update_init(void) return -ENOMEM;
topology_inited = 1; - if (topology_update_needed) - bitmap_fill(cpumask_bits(&cpu_associativity_changes_mask), - nr_cpumask_bits); - return 0; } device_initcall(topology_update_init);