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Diffstat (limited to 'arch/powerpc/platforms/powernv/subcore.c')
-rw-r--r-- | arch/powerpc/platforms/powernv/subcore.c | 449 |
1 files changed, 449 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/powernv/subcore.c b/arch/powerpc/platforms/powernv/subcore.c new file mode 100644 index 0000000000..191424468f --- /dev/null +++ b/arch/powerpc/platforms/powernv/subcore.c @@ -0,0 +1,449 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright 2013, Michael (Ellerman|Neuling), IBM Corporation. + */ + +#define pr_fmt(fmt) "powernv: " fmt + +#include <linux/kernel.h> +#include <linux/cpu.h> +#include <linux/cpumask.h> +#include <linux/device.h> +#include <linux/gfp.h> +#include <linux/smp.h> +#include <linux/stop_machine.h> + +#include <asm/cputhreads.h> +#include <asm/cpuidle.h> +#include <asm/kvm_ppc.h> +#include <asm/machdep.h> +#include <asm/opal.h> +#include <asm/smp.h> + +#include <trace/events/ipi.h> + +#include "subcore.h" +#include "powernv.h" + + +/* + * Split/unsplit procedure: + * + * A core can be in one of three states, unsplit, 2-way split, and 4-way split. + * + * The mapping to subcores_per_core is simple: + * + * State | subcores_per_core + * ------------|------------------ + * Unsplit | 1 + * 2-way split | 2 + * 4-way split | 4 + * + * The core is split along thread boundaries, the mapping between subcores and + * threads is as follows: + * + * Unsplit: + * ---------------------------- + * Subcore | 0 | + * ---------------------------- + * Thread | 0 1 2 3 4 5 6 7 | + * ---------------------------- + * + * 2-way split: + * ------------------------------------- + * Subcore | 0 | 1 | + * ------------------------------------- + * Thread | 0 1 2 3 | 4 5 6 7 | + * ------------------------------------- + * + * 4-way split: + * ----------------------------------------- + * Subcore | 0 | 1 | 2 | 3 | + * ----------------------------------------- + * Thread | 0 1 | 2 3 | 4 5 | 6 7 | + * ----------------------------------------- + * + * + * Transitions + * ----------- + * + * It is not possible to transition between either of the split states, the + * core must first be unsplit. The legal transitions are: + * + * ----------- --------------- + * | | <----> | 2-way split | + * | | --------------- + * | Unsplit | + * | | --------------- + * | | <----> | 4-way split | + * ----------- --------------- + * + * Unsplitting + * ----------- + * + * Unsplitting is the simpler procedure. It requires thread 0 to request the + * unsplit while all other threads NAP. + * + * Thread 0 clears HID0_POWER8_DYNLPARDIS (Dynamic LPAR Disable). This tells + * the hardware that if all threads except 0 are napping, the hardware should + * unsplit the core. + * + * Non-zero threads are sent to a NAP loop, they don't exit the loop until they + * see the core unsplit. + * + * Core 0 spins waiting for the hardware to see all the other threads napping + * and perform the unsplit. + * + * Once thread 0 sees the unsplit, it IPIs the secondary threads to wake them + * out of NAP. They will then see the core unsplit and exit the NAP loop. + * + * Splitting + * --------- + * + * The basic splitting procedure is fairly straight forward. However it is + * complicated by the fact that after the split occurs, the newly created + * subcores are not in a fully initialised state. + * + * Most notably the subcores do not have the correct value for SDR1, which + * means they must not be running in virtual mode when the split occurs. The + * subcores have separate timebases SPRs but these are pre-synchronised by + * opal. + * + * To begin with secondary threads are sent to an assembly routine. There they + * switch to real mode, so they are immune to the uninitialised SDR1 value. + * Once in real mode they indicate that they are in real mode, and spin waiting + * to see the core split. + * + * Thread 0 waits to see that all secondaries are in real mode, and then begins + * the splitting procedure. It firstly sets HID0_POWER8_DYNLPARDIS, which + * prevents the hardware from unsplitting. Then it sets the appropriate HID bit + * to request the split, and spins waiting to see that the split has happened. + * + * Concurrently the secondaries will notice the split. When they do they set up + * their SPRs, notably SDR1, and then they can return to virtual mode and exit + * the procedure. + */ + +/* Initialised at boot by subcore_init() */ +static int subcores_per_core; + +/* + * Used to communicate to offline cpus that we want them to pop out of the + * offline loop and do a split or unsplit. + * + * 0 - no split happening + * 1 - unsplit in progress + * 2 - split to 2 in progress + * 4 - split to 4 in progress + */ +static int new_split_mode; + +static cpumask_var_t cpu_offline_mask; + +struct split_state { + u8 step; + u8 master; +}; + +static DEFINE_PER_CPU(struct split_state, split_state); + +static void wait_for_sync_step(int step) +{ + int i, cpu = smp_processor_id(); + + for (i = cpu + 1; i < cpu + threads_per_core; i++) + while(per_cpu(split_state, i).step < step) + barrier(); + + /* Order the wait loop vs any subsequent loads/stores. */ + mb(); +} + +static void update_hid_in_slw(u64 hid0) +{ + u64 idle_states = pnv_get_supported_cpuidle_states(); + + if (idle_states & OPAL_PM_WINKLE_ENABLED) { + /* OPAL call to patch slw with the new HID0 value */ + u64 cpu_pir = hard_smp_processor_id(); + + opal_slw_set_reg(cpu_pir, SPRN_HID0, hid0); + } +} + +static inline void update_power8_hid0(unsigned long hid0) +{ + /* + * The HID0 update on Power8 should at the very least be + * preceded by a SYNC instruction followed by an ISYNC + * instruction + */ + asm volatile("sync; mtspr %0,%1; isync":: "i"(SPRN_HID0), "r"(hid0)); +} + +static void unsplit_core(void) +{ + u64 hid0, mask; + int i, cpu; + + mask = HID0_POWER8_2LPARMODE | HID0_POWER8_4LPARMODE; + + cpu = smp_processor_id(); + if (cpu_thread_in_core(cpu) != 0) { + while (mfspr(SPRN_HID0) & mask) + power7_idle_type(PNV_THREAD_NAP); + + per_cpu(split_state, cpu).step = SYNC_STEP_UNSPLIT; + return; + } + + hid0 = mfspr(SPRN_HID0); + hid0 &= ~HID0_POWER8_DYNLPARDIS; + update_power8_hid0(hid0); + update_hid_in_slw(hid0); + + while (mfspr(SPRN_HID0) & mask) + cpu_relax(); + + /* Wake secondaries out of NAP */ + for (i = cpu + 1; i < cpu + threads_per_core; i++) + smp_send_reschedule(i); + + wait_for_sync_step(SYNC_STEP_UNSPLIT); +} + +static void split_core(int new_mode) +{ + struct { u64 value; u64 mask; } split_parms[2] = { + { HID0_POWER8_1TO2LPAR, HID0_POWER8_2LPARMODE }, + { HID0_POWER8_1TO4LPAR, HID0_POWER8_4LPARMODE } + }; + int i, cpu; + u64 hid0; + + /* Convert new_mode (2 or 4) into an index into our parms array */ + i = (new_mode >> 1) - 1; + BUG_ON(i < 0 || i > 1); + + cpu = smp_processor_id(); + if (cpu_thread_in_core(cpu) != 0) { + split_core_secondary_loop(&per_cpu(split_state, cpu).step); + return; + } + + wait_for_sync_step(SYNC_STEP_REAL_MODE); + + /* Write new mode */ + hid0 = mfspr(SPRN_HID0); + hid0 |= HID0_POWER8_DYNLPARDIS | split_parms[i].value; + update_power8_hid0(hid0); + update_hid_in_slw(hid0); + + /* Wait for it to happen */ + while (!(mfspr(SPRN_HID0) & split_parms[i].mask)) + cpu_relax(); +} + +static void cpu_do_split(int new_mode) +{ + /* + * At boot subcores_per_core will be 0, so we will always unsplit at + * boot. In the usual case where the core is already unsplit it's a + * nop, and this just ensures the kernel's notion of the mode is + * consistent with the hardware. + */ + if (subcores_per_core != 1) + unsplit_core(); + + if (new_mode != 1) + split_core(new_mode); + + mb(); + per_cpu(split_state, smp_processor_id()).step = SYNC_STEP_FINISHED; +} + +bool cpu_core_split_required(void) +{ + smp_rmb(); + + if (!new_split_mode) + return false; + + cpu_do_split(new_split_mode); + + return true; +} + +void update_subcore_sibling_mask(void) +{ + int cpu; + /* + * sibling mask for the first cpu. Left shift this by required bits + * to get sibling mask for the rest of the cpus. + */ + int sibling_mask_first_cpu = (1 << threads_per_subcore) - 1; + + for_each_possible_cpu(cpu) { + int tid = cpu_thread_in_core(cpu); + int offset = (tid / threads_per_subcore) * threads_per_subcore; + int mask = sibling_mask_first_cpu << offset; + + paca_ptrs[cpu]->subcore_sibling_mask = mask; + + } +} + +static int cpu_update_split_mode(void *data) +{ + int cpu, new_mode = *(int *)data; + + if (this_cpu_ptr(&split_state)->master) { + new_split_mode = new_mode; + smp_wmb(); + + cpumask_andnot(cpu_offline_mask, cpu_present_mask, + cpu_online_mask); + + /* This should work even though the cpu is offline */ + for_each_cpu(cpu, cpu_offline_mask) + smp_send_reschedule(cpu); + } + + cpu_do_split(new_mode); + + if (this_cpu_ptr(&split_state)->master) { + /* Wait for all cpus to finish before we touch subcores_per_core */ + for_each_present_cpu(cpu) { + if (cpu >= setup_max_cpus) + break; + + while(per_cpu(split_state, cpu).step < SYNC_STEP_FINISHED) + barrier(); + } + + new_split_mode = 0; + + /* Make the new mode public */ + subcores_per_core = new_mode; + threads_per_subcore = threads_per_core / subcores_per_core; + update_subcore_sibling_mask(); + + /* Make sure the new mode is written before we exit */ + mb(); + } + + return 0; +} + +static int set_subcores_per_core(int new_mode) +{ + struct split_state *state; + int cpu; + + if (kvm_hv_mode_active()) { + pr_err("Unable to change split core mode while KVM active.\n"); + return -EBUSY; + } + + /* + * We are only called at boot, or from the sysfs write. If that ever + * changes we'll need a lock here. + */ + BUG_ON(new_mode < 1 || new_mode > 4 || new_mode == 3); + + for_each_present_cpu(cpu) { + state = &per_cpu(split_state, cpu); + state->step = SYNC_STEP_INITIAL; + state->master = 0; + } + + cpus_read_lock(); + + /* This cpu will update the globals before exiting stop machine */ + this_cpu_ptr(&split_state)->master = 1; + + /* Ensure state is consistent before we call the other cpus */ + mb(); + + stop_machine_cpuslocked(cpu_update_split_mode, &new_mode, + cpu_online_mask); + + cpus_read_unlock(); + + return 0; +} + +static ssize_t __used store_subcores_per_core(struct device *dev, + struct device_attribute *attr, const char *buf, + size_t count) +{ + unsigned long val; + int rc; + + /* We are serialised by the attribute lock */ + + rc = sscanf(buf, "%lx", &val); + if (rc != 1) + return -EINVAL; + + switch (val) { + case 1: + case 2: + case 4: + if (subcores_per_core == val) + /* Nothing to do */ + goto out; + break; + default: + return -EINVAL; + } + + rc = set_subcores_per_core(val); + if (rc) + return rc; + +out: + return count; +} + +static ssize_t show_subcores_per_core(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "%x\n", subcores_per_core); +} + +static DEVICE_ATTR(subcores_per_core, 0644, + show_subcores_per_core, store_subcores_per_core); + +static int subcore_init(void) +{ + struct device *dev_root; + unsigned pvr_ver; + int rc = 0; + + pvr_ver = PVR_VER(mfspr(SPRN_PVR)); + + if (pvr_ver != PVR_POWER8 && + pvr_ver != PVR_POWER8E && + pvr_ver != PVR_POWER8NVL) + return 0; + + /* + * We need all threads in a core to be present to split/unsplit so + * continue only if max_cpus are aligned to threads_per_core. + */ + if (setup_max_cpus % threads_per_core) + return 0; + + BUG_ON(!alloc_cpumask_var(&cpu_offline_mask, GFP_KERNEL)); + + set_subcores_per_core(1); + + dev_root = bus_get_dev_root(&cpu_subsys); + if (dev_root) { + rc = device_create_file(dev_root, &dev_attr_subcores_per_core); + put_device(dev_root); + } + return rc; +} +machine_device_initcall(powernv, subcore_init); |