Messages in this thread Patch in this message |  | | From | Srikar Dronamraju <> | Subject | [PATCH] sched/topology: Use Identity node only if required | Date | Wed, 8 Aug 2018 12:39:31 +0530 |
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With Commit 051f3ca02e46 ("sched/topology: Introduce NUMA identity node sched domain") scheduler introduces an extra numa level. However that leads to
- numa topology on 2 node systems no more marked as NUMA_DIRECT. After this commit, it gets reported as NUMA_BACKPLANE. This is because sched_domains_numa_level now equals 2 on 2 node systems.
- Extra numa sched domain that gets added and degenerated on most machines. The Identity node is only needed on very few systems. Also all non-numa systems will end up populating sched_domains_numa_distance and sched_domains_numa_masks tables.
- On shared lpars like powerpc, this extra sched domain creation can lead to repeated rcu stalls, sometimes even causing unresponsive systems on boot. On such stalls, it was noticed that init_sched_groups_capacity() (sg != sd->groups is always true).
INFO: rcu_sched self-detected stall on CPU 1-....: (240039 ticks this GP) idle=c32/1/4611686018427387906 softirq=782/782 fqs=80012 (t=240039 jiffies g=6272 c=6271 q=263040) NMI backtrace for cpu 1 CPU: 1 PID: 1576 Comm: kworker/1:1 Kdump: loaded Tainted: G E 4.18.0-rc7-master+ #42 Workqueue: events topology_work_fn Call Trace: [c00000832132f190] [c0000000009557ac] dump_stack+0xb0/0xf4 (unreliable) [c00000832132f1d0] [c00000000095ed54] nmi_cpu_backtrace+0x1b4/0x230 [c00000832132f270] [c00000000095efac] nmi_trigger_cpumask_backtrace+0x1dc/0x220 [c00000832132f310] [c00000000005f77c] arch_trigger_cpumask_backtrace+0x2c/0x40 [c00000832132f330] [c0000000001a32d4] rcu_dump_cpu_stacks+0x100/0x15c [c00000832132f380] [c0000000001a2024] rcu_check_callbacks+0x894/0xaa0 [c00000832132f4a0] [c0000000001ace9c] update_process_times+0x4c/0xa0 [c00000832132f4d0] [c0000000001c5400] tick_sched_handle.isra.13+0x50/0x80 [c00000832132f4f0] [c0000000001c549c] tick_sched_timer+0x6c/0xd0 [c00000832132f530] [c0000000001ae044] __hrtimer_run_queues+0x134/0x360 [c00000832132f5b0] [c0000000001aeea4] hrtimer_interrupt+0x124/0x300 [c00000832132f660] [c000000000024a04] timer_interrupt+0x114/0x2f0 [c00000832132f6c0] [c0000000000090f4] decrementer_common+0x114/0x120 --- interrupt: 901 at __bitmap_weight+0x70/0x100 LR = __bitmap_weight+0x78/0x100 [c00000832132f9b0] [c0000000009bb738] __func__.61127+0x0/0x20 (unreliable) [c00000832132fa00] [c00000000016c178] build_sched_domains+0xf98/0x13f0 [c00000832132fb30] [c00000000016d73c] partition_sched_domains+0x26c/0x440 [c00000832132fc20] [c0000000001ee284] rebuild_sched_domains_locked+0x64/0x80 [c00000832132fc50] [c0000000001f11ec] rebuild_sched_domains+0x3c/0x60 [c00000832132fc80] [c00000000007e1c4] topology_work_fn+0x24/0x40 [c00000832132fca0] [c000000000126704] process_one_work+0x1a4/0x470 [c00000832132fd30] [c000000000126a68] worker_thread+0x98/0x540 [c00000832132fdc0] [c00000000012f078] kthread+0x168/0x1b0 [c00000832132fe30] [c00000000000b65c] ret_from_kernel_thread+0x5c/0x80
Similar problem was earlier also reported at https://lwn.net/ml/linux-kernel/20180512100233.GB3738@osiris/
One easy alternative would be to use a hint from architectures that have a liking for identity node.
Fixes: 051f3ca02e46 "Introduce NUMA identity node sched domain" Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> --- arch/x86/include/asm/topology.h | 2 ++ arch/x86/kernel/smpboot.c | 5 +++++ kernel/sched/topology.c | 34 ++++++++++++++++++++++++---------- 3 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h index c1d2a9892352..524cb900e273 100644 --- a/arch/x86/include/asm/topology.h +++ b/arch/x86/include/asm/topology.h @@ -79,7 +79,9 @@ extern void setup_node_to_cpumask_map(void); extern int __node_distance(int, int); #define node_distance(a, b) __node_distance(a, b) +#define arch_supports_identity_node arch_supports_identity_node +extern int arch_supports_identity_node(void); #else /* !CONFIG_NUMA */ static inline int numa_node_id(void) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index db9656e13ea0..08de8ca06232 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1346,6 +1346,11 @@ void __init native_smp_cpus_done(unsigned int max_cpus) mtrr_aps_init(); } +int arch_supports_identity_node(void) +{ + return x86_has_numa_in_package; +} + static int __initdata setup_possible_cpus = -1; static int __init _setup_possible_cpus(char *str) { diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 56a0fed30c0a..8f61df23948a 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1322,20 +1322,30 @@ static void init_numa_topology_type(void) } } +#ifndef arch_supports_identity_node +static inline int arch_supports_identity_node(void) +{ + return 0; +} +#endif + void sched_init_numa(void) { int next_distance, curr_distance = node_distance(0, 0); struct sched_domain_topology_level *tl; - int level = 0; + int numa_in_package, level = 0; int i, j, k; sched_domains_numa_distance = kzalloc(sizeof(int) * nr_node_ids, GFP_KERNEL); if (!sched_domains_numa_distance) return; - /* Includes NUMA identity node at level 0. */ - sched_domains_numa_distance[level++] = curr_distance; - sched_domains_numa_levels = level; + numa_in_package = arch_supports_identity_node(); + if (numa_in_package) { + /* Includes NUMA identity node at level 0. */ + sched_domains_numa_distance[level++] = curr_distance; + sched_domains_numa_levels = level; + } /* * O(nr_nodes^2) deduplicating selection sort -- in order to find the @@ -1445,19 +1455,23 @@ void sched_init_numa(void) for (i = 0; sched_domain_topology[i].mask; i++) tl[i] = sched_domain_topology[i]; + j = 0; /* * Add the NUMA identity distance, aka single NODE. */ - tl[i++] = (struct sched_domain_topology_level){ - .mask = sd_numa_mask, - .numa_level = 0, - SD_INIT_NAME(NODE) - }; + if (numa_in_package) { + tl[i++] = (struct sched_domain_topology_level){ + .mask = sd_numa_mask, + .numa_level = 0, + SD_INIT_NAME(NODE) + }; + j++; + } /* * .. and append 'j' levels of NUMA goodness. */ - for (j = 1; j < level; i++, j++) { + for (; j < level; i++, j++) { tl[i] = (struct sched_domain_topology_level){ .mask = sd_numa_mask, .sd_flags = cpu_numa_flags, -- 2.12.3
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