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/alpha/boot/main.c | 190 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 190 insertions(+) create mode 100644 arch/alpha/boot/main.c (limited to 'arch/alpha/boot/main.c') diff --git a/arch/alpha/boot/main.c b/arch/alpha/boot/main.c new file mode 100644 index 000000000..22a1cb026 --- /dev/null +++ b/arch/alpha/boot/main.c @@ -0,0 +1,190 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * arch/alpha/boot/main.c + * + * Copyright (C) 1994, 1995 Linus Torvalds + * + * This file is the bootloader for the Linux/AXP kernel + */ +#include +#include +#include +#include +#include + +#include +#include + +#include + +#include "ksize.h" + +extern unsigned long switch_to_osf_pal(unsigned long nr, + struct pcb_struct * pcb_va, struct pcb_struct * pcb_pa, + unsigned long *vptb); +struct hwrpb_struct *hwrpb = INIT_HWRPB; +static struct pcb_struct pcb_va[1]; + +/* + * Find a physical address of a virtual object.. + * + * This is easy using the virtual page table address. + */ + +static inline void * +find_pa(unsigned long *vptb, void *ptr) +{ + unsigned long address = (unsigned long) ptr; + unsigned long result; + + result = vptb[address >> 13]; + result >>= 32; + result <<= 13; + result |= address & 0x1fff; + return (void *) result; +} + +/* + * This function moves into OSF/1 pal-code, and has a temporary + * PCB for that. The kernel proper should replace this PCB with + * the real one as soon as possible. + * + * The page table muckery in here depends on the fact that the boot + * code has the L1 page table identity-map itself in the second PTE + * in the L1 page table. Thus the L1-page is virtually addressable + * itself (through three levels) at virtual address 0x200802000. + */ + +#define VPTB ((unsigned long *) 0x200000000) +#define L1 ((unsigned long *) 0x200802000) + +void +pal_init(void) +{ + unsigned long i, rev; + struct percpu_struct * percpu; + struct pcb_struct * pcb_pa; + + /* Create the dummy PCB. */ + pcb_va->ksp = 0; + pcb_va->usp = 0; + pcb_va->ptbr = L1[1] >> 32; + pcb_va->asn = 0; + pcb_va->pcc = 0; + pcb_va->unique = 0; + pcb_va->flags = 1; + pcb_va->res1 = 0; + pcb_va->res2 = 0; + pcb_pa = find_pa(VPTB, pcb_va); + + /* + * a0 = 2 (OSF) + * a1 = return address, but we give the asm the vaddr of the PCB + * a2 = physical addr of PCB + * a3 = new virtual page table pointer + * a4 = KSP (but the asm sets it) + */ + srm_printk("Switching to OSF PAL-code .. "); + + i = switch_to_osf_pal(2, pcb_va, pcb_pa, VPTB); + if (i) { + srm_printk("failed, code %ld\n", i); + __halt(); + } + + percpu = (struct percpu_struct *) + (INIT_HWRPB->processor_offset + (unsigned long) INIT_HWRPB); + rev = percpu->pal_revision = percpu->palcode_avail[2]; + + srm_printk("Ok (rev %lx)\n", rev); + + tbia(); /* do it directly in case we are SMP */ +} + +static inline long openboot(void) +{ + char bootdev[256]; + long result; + + result = callback_getenv(ENV_BOOTED_DEV, bootdev, 255); + if (result < 0) + return result; + return callback_open(bootdev, result & 255); +} + +static inline long close(long dev) +{ + return callback_close(dev); +} + +static inline long load(long dev, unsigned long addr, unsigned long count) +{ + char bootfile[256]; + extern char _end; + long result, boot_size = &_end - (char *) BOOT_ADDR; + + result = callback_getenv(ENV_BOOTED_FILE, bootfile, 255); + if (result < 0) + return result; + result &= 255; + bootfile[result] = '\0'; + if (result) + srm_printk("Boot file specification (%s) not implemented\n", + bootfile); + return callback_read(dev, count, (void *)addr, boot_size/512 + 1); +} + +/* + * Start the kernel. + */ +static void runkernel(void) +{ + __asm__ __volatile__( + "bis %1,%1,$30\n\t" + "bis %0,%0,$26\n\t" + "ret ($26)" + : /* no outputs: it doesn't even return */ + : "r" (START_ADDR), + "r" (PAGE_SIZE + INIT_STACK)); +} + +void start_kernel(void) +{ + long i; + long dev; + int nbytes; + char envval[256]; + + srm_printk("Linux/AXP bootloader for Linux " UTS_RELEASE "\n"); + if (INIT_HWRPB->pagesize != 8192) { + srm_printk("Expected 8kB pages, got %ldkB\n", INIT_HWRPB->pagesize >> 10); + return; + } + pal_init(); + dev = openboot(); + if (dev < 0) { + srm_printk("Unable to open boot device: %016lx\n", dev); + return; + } + dev &= 0xffffffff; + srm_printk("Loading vmlinux ..."); + i = load(dev, START_ADDR, KERNEL_SIZE); + close(dev); + if (i != KERNEL_SIZE) { + srm_printk("Failed (%lx)\n", i); + return; + } + + nbytes = callback_getenv(ENV_BOOTED_OSFLAGS, envval, sizeof(envval)); + if (nbytes < 0) { + nbytes = 0; + } + envval[nbytes] = '\0'; + strcpy((char*)ZERO_PGE, envval); + + srm_printk(" Ok\nNow booting the kernel\n"); + runkernel(); + for (i = 0 ; i < 0x100000000 ; i++) + /* nothing */; + __halt(); +} -- cgit v1.3.1