From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- arch/powerpc/boot/simpleboot.c | 87 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 87 insertions(+) create mode 100644 arch/powerpc/boot/simpleboot.c (limited to 'arch/powerpc/boot/simpleboot.c') diff --git a/arch/powerpc/boot/simpleboot.c b/arch/powerpc/boot/simpleboot.c new file mode 100644 index 000000000..27591df41 --- /dev/null +++ b/arch/powerpc/boot/simpleboot.c @@ -0,0 +1,87 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * The simple platform -- for booting when firmware doesn't supply a device + * tree or any platform configuration information. + * All data is extracted from an embedded device tree + * blob. + * + * Authors: Scott Wood + * Grant Likely + * + * Copyright (c) 2007 Freescale Semiconductor, Inc. + * Copyright (c) 2008 Secret Lab Technologies Ltd. + */ + +#include "ops.h" +#include "types.h" +#include "io.h" +#include "stdio.h" +#include + +BSS_STACK(4*1024); + +extern int platform_specific_init(void) __attribute__((weak)); + +void platform_init(unsigned long r3, unsigned long r4, unsigned long r5, + unsigned long r6, unsigned long r7) +{ + const u32 *na, *ns, *reg, *timebase; + u64 memsize64; + int node, size, i; + + /* Make sure FDT blob is sane */ + if (fdt_check_header(_dtb_start) != 0) + fatal("Invalid device tree blob\n"); + + /* Find the #address-cells and #size-cells properties */ + node = fdt_path_offset(_dtb_start, "/"); + if (node < 0) + fatal("Cannot find root node\n"); + na = fdt_getprop(_dtb_start, node, "#address-cells", &size); + if (!na || (size != 4)) + fatal("Cannot find #address-cells property"); + ns = fdt_getprop(_dtb_start, node, "#size-cells", &size); + if (!ns || (size != 4)) + fatal("Cannot find #size-cells property"); + + /* Find the memory range */ + node = fdt_node_offset_by_prop_value(_dtb_start, -1, "device_type", + "memory", sizeof("memory")); + if (node < 0) + fatal("Cannot find memory node\n"); + reg = fdt_getprop(_dtb_start, node, "reg", &size); + if (size < (*na+*ns) * sizeof(u32)) + fatal("cannot get memory range\n"); + + /* Only interested in memory based at 0 */ + for (i = 0; i < *na; i++) + if (*reg++ != 0) + fatal("Memory range is not based at address 0\n"); + + /* get the memsize and truncate it to under 4G on 32 bit machines */ + memsize64 = 0; + for (i = 0; i < *ns; i++) + memsize64 = (memsize64 << 32) | *reg++; + if (sizeof(void *) == 4 && memsize64 >= 0x100000000ULL) + memsize64 = 0xffffffff; + + /* finally, setup the timebase */ + node = fdt_node_offset_by_prop_value(_dtb_start, -1, "device_type", + "cpu", sizeof("cpu")); + if (node < 0) + fatal("Cannot find cpu node\n"); + timebase = fdt_getprop(_dtb_start, node, "timebase-frequency", &size); + if (timebase && (size == 4)) + timebase_period_ns = 1000000000 / *timebase; + + /* Now we have the memory size; initialize the heap */ + simple_alloc_init(_end, memsize64 - (unsigned long)_end, 32, 64); + + /* prepare the device tree and find the console */ + fdt_init(_dtb_start); + + if (platform_specific_init) + platform_specific_init(); + + serial_console_init(); +} -- cgit v1.3.1