kernel.git/arch/powerpc/kernel/smp.c, branch linux-5.13.y

powerpc/smp: Update cpu_core_map on all PowerPc systems

2021-09-18T11:41:56Z

[ Upstream commit b8b928030332a0ca16d42433eb2c3085600d8704 ] lscpu() uses core_siblings to list the number of sockets in the system. core_siblings is set using topology_core_cpumask. While optimizing the powerpc bootup path, Commit 4ca234a9cbd7 ("powerpc/smp: Stop updating cpu_core_mask"). it was found that updating cpu_core_mask() ended up taking a lot of time. It was thought that on Powerpc, cpu_core_mask() would always be same as cpu_cpu_mask() i.e number of sockets will always be equal to number of nodes. As an optimization, cpu_core_mask() was made a snapshot of cpu_cpu_mask(). However that was found to be false with PowerPc KVM guests, where each node could have more than one socket. So with Commit c47f892d7aa6 ("powerpc/smp: Reintroduce cpu_core_mask"), cpu_core_mask was updated based on chip_id but in an optimized way using some mask manipulations and chip_id caching. However on non-PowerNV and non-pseries KVM guests (i.e not implementing cpu_to_chip_id(), continued to use a copy of cpu_cpu_mask(). There are two issues that were noticed on such systems 1. lscpu would report one extra socket. On a IBM,9009-42A (aka zz system) which has only 2 chips/ sockets/ nodes, lscpu would report Architecture: ppc64le Byte Order: Little Endian CPU(s): 160 On-line CPU(s) list: 0-159 Thread(s) per core: 8 Core(s) per socket: 6 Socket(s): 3 <-------------- NUMA node(s): 2 Model: 2.2 (pvr 004e 0202) Model name: POWER9 (architected), altivec supported Hypervisor vendor: pHyp Virtualization type: para L1d cache: 32K L1i cache: 32K L2 cache: 512K L3 cache: 10240K NUMA node0 CPU(s): 0-79 NUMA node1 CPU(s): 80-159 2. Currently cpu_cpu_mask is updated when a core is added/removed. However its not updated when smt mode switching or on CPUs are explicitly offlined. However all other percpu masks are updated to ensure only active/online CPUs are in the masks. This results in build_sched_domain traces since there will be CPUs in cpu_cpu_mask() but those CPUs are not present in SMT / CACHE / MC / NUMA domains. A loop of threads running smt mode switching and core add/remove will soon show this trace. Hence cpu_cpu_mask has to be update at smt mode switch. This will have impact on cpu_core_mask(). cpu_core_mask() is a snapshot of cpu_cpu_mask. Different CPUs within the same socket will end up having different cpu_core_masks since they are snapshots at different points of time. This means when lscpu will start reporting many more sockets than the actual number of sockets/ nodes / chips. Different ways to handle this problem: A. Update the snapshot aka cpu_core_mask for all CPUs whenever cpu_cpu_mask is updated. This would a non-optimal solution. B. Instead of a cpumask_var_t, make cpu_core_map a cpumask pointer pointing to cpu_cpu_mask. However percpu cpumask pointer is frowned upon and we need a clean way to handle PowerPc KVM guest which is not a snapshot. C. Update cpu_core_masks all PowerPc systems like in PowerPc KVM guests using mask manipulations. This approach is relatively simple and unifies with the existing code. D. On top of 3, we could also resurrect get_physical_package_id which could return a nid for the said CPU. However this is not needed at this time. Option C is the preferred approach for now. While this is somewhat a revert of Commit 4ca234a9cbd7 ("powerpc/smp: Stop updating cpu_core_mask"). 1. Plain revert has some conflicts 2. For chip_id == -1, the cpu_core_mask is made identical to cpu_cpu_mask, unlike previously where cpu_core_mask was set to a core if chip_id doesn't exist. This goes by the principle that if chip_id is not exposed, then sockets / chip / node share the same set of CPUs. With the fix, lscpu o/p would be Architecture: ppc64le Byte Order: Little Endian CPU(s): 160 On-line CPU(s) list: 0-159 Thread(s) per core: 8 Core(s) per socket: 6 Socket(s): 2 <-------------- NUMA node(s): 2 Model: 2.2 (pvr 004e 0202) Model name: POWER9 (architected), altivec supported Hypervisor vendor: pHyp Virtualization type: para L1d cache: 32K L1i cache: 32K L2 cache: 512K L3 cache: 10240K NUMA node0 CPU(s): 0-79 NUMA node1 CPU(s): 80-159 Fixes: 4ca234a9cbd7 ("powerpc/smp: Stop updating cpu_core_mask") Signed-off-by: Srikar Dronamraju Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210826100401.412519-3-srikar@linux.vnet.ibm.com Signed-off-by: Sasha Levin

powerpc/smp: Fix a crash while booting kvm guest with nr_cpus=2

2021-09-18T11:41:56Z

[ Upstream commit 8efd249babea2fec268cff90b9f5ca723dbb7499 ] Aneesh reported a crash with a fairly recent upstream kernel when booting kernel whose commandline was appended with nr_cpus=2 1:mon> e cpu 0x1: Vector: 300 (Data Access) at [c000000008a67bd0] pc: c00000000002557c: cpu_to_chip_id+0x3c/0x100 lr: c000000000058380: start_secondary+0x460/0xb00 sp: c000000008a67e70 msr: 8000000000001033 dar: 10 dsisr: 80000 current = 0xc00000000891bb00 paca = 0xc0000018ff981f80 irqmask: 0x03 irq_happened: 0x01 pid = 0, comm = swapper/1 Linux version 5.13.0-rc3-15704-ga050a6d2b7e8 (kvaneesh@ltc-boston8) (gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #433 SMP Tue May 25 02:38:49 CDT 2021 1:mon> t [link register ] c000000000058380 start_secondary+0x460/0xb00 [c000000008a67e70] c000000008a67eb0 (unreliable) [c000000008a67eb0] c0000000000589d4 start_secondary+0xab4/0xb00 [c000000008a67f90] c00000000000c654 start_secondary_prolog+0x10/0x14 Current code assumes that num_possible_cpus() is always greater than threads_per_core. However this may not be true when using nr_cpus=2 or similar options. Handle the case where num_possible_cpus() is not an exact multiple of threads_per_core. Fixes: c1e53367dab1 ("powerpc/smp: Cache CPU to chip lookup") Reported-by: Aneesh Kumar K.V Signed-off-by: Srikar Dronamraju Debugged-by: Michael Ellerman Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210826100401.412519-2-srikar@linux.vnet.ibm.com Signed-off-by: Sasha Levin

powerpc: Offline CPU in stop_this_cpu()

2021-07-14T15:07:45Z

[ Upstream commit bab26238bbd44d5a4687c0a64fd2c7f2755ea937 ] printk_safe_flush_on_panic() has special lock breaking code for the case where we panic()ed with the console lock held. It relies on panic IPI causing other CPUs to mark themselves offline. Do as most other architectures do. This effectively reverts commit de6e5d38417e ("powerpc: smp_send_stop do not offline stopped CPUs"), unfortunately it may result in some false positive warnings, but the alternative is more situations where we can crash without getting messages out. Fixes: de6e5d38417e ("powerpc: smp_send_stop do not offline stopped CPUs") Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210623041245.865134-1-npiggin@gmail.com Signed-off-by: Sasha Levin

sched/core: Initialize the idle task with preemption disabled

2021-07-14T15:06:21Z

[ Upstream commit f1a0a376ca0c4ef1fc3d24e3e502acbb5b795674 ] As pointed out by commit de9b8f5dcbd9 ("sched: Fix crash trying to dequeue/enqueue the idle thread") init_idle() can and will be invoked more than once on the same idle task. At boot time, it is invoked for the boot CPU thread by sched_init(). Then smp_init() creates the threads for all the secondary CPUs and invokes init_idle() on them. As the hotplug machinery brings the secondaries to life, it will issue calls to idle_thread_get(), which itself invokes init_idle() yet again. In this case it's invoked twice more per secondary: at _cpu_up(), and at bringup_cpu(). Given smp_init() already initializes the idle tasks for all *possible* CPUs, no further initialization should be required. Now, removing init_idle() from idle_thread_get() exposes some interesting expectations with regards to the idle task's preempt_count: the secondary startup always issues a preempt_disable(), requiring some reset of the preempt count to 0 between hot-unplug and hotplug, which is currently served by idle_thread_get() -> idle_init(). Given the idle task is supposed to have preemption disabled once and never see it re-enabled, it seems that what we actually want is to initialize its preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove init_idle() from idle_thread_get(). Secondary startups were patched via coccinelle: @begone@ @@ -preempt_disable(); ... cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); Signed-off-by: Valentin Schneider Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Link: https://lore.kernel.org/r/20210512094636.2958515-1-valentin.schneider@arm.com Signed-off-by: Sasha Levin

powerpc/smp: Set numa node before updating mask

2021-04-17T12:46:31Z

Geethika reported a trace when doing a dlpar CPU add. ------------[ cut here ]------------ WARNING: CPU: 152 PID: 1134 at kernel/sched/topology.c:2057 CPU: 152 PID: 1134 Comm: kworker/152:1 Not tainted 5.12.0-rc5-master #5 Workqueue: events cpuset_hotplug_workfn NIP: c0000000001cfc14 LR: c0000000001cfc10 CTR: c0000000007e3420 REGS: c0000034a08eb260 TRAP: 0700 Not tainted (5.12.0-rc5-master+) MSR: 8000000000029033 CR: 28828422 XER: 00000020 CFAR: c0000000001fd888 IRQMASK: 0 #012GPR00: c0000000001cfc10 c0000034a08eb500 c000000001f35400 0000000000000027 #012GPR04: c0000035abaa8010 c0000035abb30a00 0000000000000027 c0000035abaa8018 #012GPR08: 0000000000000023 c0000035abaaef48 00000035aa540000 c0000035a49dffe8 #012GPR12: 0000000028828424 c0000035bf1a1c80 0000000000000497 0000000000000004 #012GPR16: c00000000347a258 0000000000000140 c00000000203d468 c000000001a1a490 #012GPR20: c000000001f9c160 c0000034adf70920 c0000034aec9fd20 0000000100087bd3 #012GPR24: 0000000100087bd3 c0000035b3de09f8 0000000000000030 c0000035b3de09f8 #012GPR28: 0000000000000028 c00000000347a280 c0000034aefe0b00 c0000000010a2a68 NIP [c0000000001cfc14] build_sched_domains+0x6a4/0x1500 LR [c0000000001cfc10] build_sched_domains+0x6a0/0x1500 Call Trace: [c0000034a08eb500] [c0000000001cfc10] build_sched_domains+0x6a0/0x1500 (unreliable) [c0000034a08eb640] [c0000000001d1e6c] partition_sched_domains_locked+0x3ec/0x530 [c0000034a08eb6e0] [c0000000002936d4] rebuild_sched_domains_locked+0x524/0xbf0 [c0000034a08eb7e0] [c000000000296bb0] rebuild_sched_domains+0x40/0x70 [c0000034a08eb810] [c000000000296e74] cpuset_hotplug_workfn+0x294/0xe20 [c0000034a08ebc30] [c000000000178dd0] process_one_work+0x300/0x670 [c0000034a08ebd10] [c0000000001791b8] worker_thread+0x78/0x520 [c0000034a08ebda0] [c000000000185090] kthread+0x1a0/0x1b0 [c0000034a08ebe10] [c00000000000ccec] ret_from_kernel_thread+0x5c/0x70 Instruction dump: 7d2903a6 4e800421 e8410018 7f67db78 7fe6fb78 7f45d378 7f84e378 7c681b78 3c62ff1a 3863c6f8 4802dc35 60000000 <0fe00000> 3920fff4 f9210070 e86100a0 ---[ end trace 532d9066d3d4d7ec ]--- Some of the per-CPU masks use cpu_cpu_mask as a filter to limit the search for related CPUs. On a dlpar add of a CPU, update cpu_cpu_mask before updating the per-CPU masks. This will ensure the cpu_cpu_mask is updated correctly before its used in setting the masks. Setting the numa_node will ensure that when cpu_cpu_mask() gets called, the correct node number is used. This code movement helped fix the above call trace. Reported-by: Geetika Moolchandani Signed-off-by: Srikar Dronamraju Reviewed-by: Nathan Lynch Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210401154200.150077-1-srikar@linux.vnet.ibm.com

powerpc/smp: Cache CPU to chip lookup

2021-04-17T00:40:51Z

On systems with large CPUs per node, even with the filtered matching of related CPUs, there can be large number of calls to cpu_to_chip_id for the same CPU. For example with 4096 vCPU, 1 node QEMU configuration, with 4 threads per core, system could be see upto 1024 calls to cpu_to_chip_id() for the same CPU. On a given system, cpu_to_chip_id() for a given CPU would always return the same. Hence cache the result in a lookup table for use in subsequent calls. Since all CPUs sharing the same core will belong to the same chip, the lookup_table has an entry for one CPU per core. chip_id_lookup_table is not being freed and would be used on subsequent CPU online post CPU offline. Reported-by: Daniel Henrique Barboza Suggested-by: Michael Ellerman Signed-off-by: Srikar Dronamraju Tested-by: Daniel Henrique Barboza Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210415120934.232271-4-srikar@linux.vnet.ibm.com

powerpc/smp: Reintroduce cpu_core_mask

2021-04-17T00:40:51Z

Daniel reported that with Commit 4ca234a9cbd7 ("powerpc/smp: Stop updating cpu_core_mask") QEMU was unable to set single NUMA node SMP topologies such as: -smp 8,maxcpus=8,cores=2,threads=2,sockets=2 i.e he expected 2 sockets in one NUMA node. The above commit helped to reduce boot time on Large Systems for example 4096 vCPU single socket QEMU instance. PAPR is silent on having more than one socket within a NUMA node. cpu_core_mask and cpu_cpu_mask for any CPU would be same unless the number of sockets is different from the number of NUMA nodes. One option is to reintroduce cpu_core_mask but use a slightly different method to arrive at the cpu_core_mask. Previously each CPU's chip-id would be compared with all other CPU's chip-id to verify if both the CPUs were related at the chip level. Now if a CPU 'A' is found related / (unrelated) to another CPU 'B', all the thread siblings of 'A' and thread siblings of 'B' are automatically marked as related / (unrelated). Also if a platform doesn't support ibm,chip-id property, i.e its cpu_to_chip_id returns -1, cpu_core_map holds a copy of cpu_cpu_mask(). Fixes: 4ca234a9cbd7 ("powerpc/smp: Stop updating cpu_core_mask") Reported-by: Daniel Henrique Barboza Signed-off-by: Srikar Dronamraju Tested-by: Daniel Henrique Barboza Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210415120934.232271-2-srikar@linux.vnet.ibm.com

powerpc/smp: Make some symbols static

2021-04-14T13:04:14Z

The sparse tool complains as follows: arch/powerpc/kernel/smp.c:86:1: warning: symbol '__pcpu_scope_cpu_coregroup_map' was not declared. Should it be static? arch/powerpc/kernel/smp.c:125:1: warning: symbol '__pcpu_scope_thread_group_l1_cache_map' was not declared. Should it be static? arch/powerpc/kernel/smp.c:132:1: warning: symbol '__pcpu_scope_thread_group_l2_cache_map' was not declared. Should it be static? These symbols are not used outside of smp.c, so this commit marks them static. Reported-by: Hulk Robot Signed-off-by: Yu Kuai Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210407125903.4139663-1-yukuai3@huawei.com

powerpc/smp: Make debugger_ipi_callback() static

2021-01-30T00:39:29Z

debugger_ipi_callback() is a local routine used as a NMI IPI handler and does not need to be external. It fixes this W=1 compile error : ../arch/powerpc/kernel/smp.c:579:6: error: no previous prototype for ‘debugger_ipi_callback’ [-Werror=missing-prototypes] 579 | void debugger_ipi_callback(struct pt_regs *regs) | ^~~~~~~~~~~~~~~~~~~~~ Signed-off-by: Cédric Le Goater Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210104143206.695198-10-clg@kaod.org

powerpc/smp: Include tick_broadcast() prototype

2021-01-30T00:39:29Z

It fixes this W=1 compile error : ../arch/powerpc/kernel/smp.c:569:6: error: no previous prototype for ‘tick_broadcast’ [-Werror=missing-prototypes] 569 | void tick_broadcast(const struct cpumask *mask) | ^~~~~~~~~~~~~~ Signed-off-by: Cédric Le Goater Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210104143206.695198-9-clg@kaod.org