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/of.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 93 insertions(+) create mode 100644 arch/powerpc/boot/of.c (limited to 'arch/powerpc/boot/of.c') diff --git a/arch/powerpc/boot/of.c b/arch/powerpc/boot/of.c new file mode 100644 index 000000000..2fbd4ae60 --- /dev/null +++ b/arch/powerpc/boot/of.c @@ -0,0 +1,93 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) Paul Mackerras 1997. + */ +#include +#include +#include "types.h" +#include "elf.h" +#include "string.h" +#include "stdio.h" +#include "page.h" +#include "ops.h" + +#include "of.h" + +/* Value picked to match that used by yaboot */ +#define PROG_START 0x01400000 /* only used on 64-bit systems */ +#define RAM_END (512<<20) /* Fixme: use OF */ +#define ONE_MB 0x100000 + + + +static unsigned long claim_base; + +void epapr_platform_init(unsigned long r3, unsigned long r4, unsigned long r5, + unsigned long r6, unsigned long r7); + +static void *of_try_claim(unsigned long size) +{ + unsigned long addr = 0; + + if (claim_base == 0) + claim_base = _ALIGN_UP((unsigned long)_end, ONE_MB); + + for(; claim_base < RAM_END; claim_base += ONE_MB) { +#ifdef DEBUG + printf(" trying: 0x%08lx\n\r", claim_base); +#endif + addr = (unsigned long) of_claim(claim_base, size, 0); + if (addr != PROM_ERROR) + break; + } + if (addr == 0) + return NULL; + claim_base = PAGE_ALIGN(claim_base + size); + return (void *)addr; +} + +static void of_image_hdr(const void *hdr) +{ + const Elf64_Ehdr *elf64 = hdr; + + if (elf64->e_ident[EI_CLASS] == ELFCLASS64) { + /* + * Maintain a "magic" minimum address. This keeps some older + * firmware platforms running. + */ + if (claim_base < PROG_START) + claim_base = PROG_START; + } +} + +static void of_platform_init(unsigned long a1, unsigned long a2, void *promptr) +{ + platform_ops.image_hdr = of_image_hdr; + platform_ops.malloc = of_try_claim; + platform_ops.exit = of_exit; + platform_ops.vmlinux_alloc = of_vmlinux_alloc; + + dt_ops.finddevice = of_finddevice; + dt_ops.getprop = of_getprop; + dt_ops.setprop = of_setprop; + + of_console_init(); + + of_init(promptr); + loader_info.promptr = promptr; + if (a1 && a2 && a2 != 0xdeadbeef) { + loader_info.initrd_addr = a1; + loader_info.initrd_size = a2; + } +} + +void platform_init(unsigned long r3, unsigned long r4, unsigned long r5, + unsigned long r6, unsigned long r7) +{ + /* Detect OF vs. ePAPR boot */ + if (r5) + of_platform_init(r3, r4, (void *)r5); + else + epapr_platform_init(r3, r4, r5, r6, r7); +} + -- cgit v1.3.1