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/opal.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 arch/powerpc/boot/opal.c (limited to 'arch/powerpc/boot/opal.c') diff --git a/arch/powerpc/boot/opal.c b/arch/powerpc/boot/opal.c new file mode 100644 index 000000000..b69818ce5 --- /dev/null +++ b/arch/powerpc/boot/opal.c @@ -0,0 +1,97 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (c) 2016 IBM Corporation. + */ + +#include "ops.h" +#include "stdio.h" +#include "io.h" +#include +#include "../include/asm/opal-api.h" + +/* Global OPAL struct used by opal-call.S */ +struct opal { + u64 base; + u64 entry; +} opal; + +static u32 opal_con_id; + +/* see opal-wrappers.S */ +int64_t opal_console_write(int64_t term_number, u64 *length, const u8 *buffer); +int64_t opal_console_read(int64_t term_number, uint64_t *length, u8 *buffer); +int64_t opal_console_write_buffer_space(uint64_t term_number, uint64_t *length); +int64_t opal_console_flush(uint64_t term_number); +int64_t opal_poll_events(uint64_t *outstanding_event_mask); + +void opal_kentry(unsigned long fdt_addr, void *vmlinux_addr); + +static int opal_con_open(void) +{ + /* + * When OPAL loads the boot kernel it stashes the OPAL base and entry + * address in r8 and r9 so the kernel can use the OPAL console + * before unflattening the devicetree. While executing the wrapper will + * probably trash r8 and r9 so this kentry hook restores them before + * entering the decompressed kernel. + */ + platform_ops.kentry = opal_kentry; + return 0; +} + +static void opal_con_putc(unsigned char c) +{ + int64_t rc; + uint64_t olen, len; + + do { + rc = opal_console_write_buffer_space(opal_con_id, &olen); + len = be64_to_cpu(olen); + if (rc) + return; + opal_poll_events(NULL); + } while (len < 1); + + + olen = cpu_to_be64(1); + opal_console_write(opal_con_id, &olen, &c); +} + +static void opal_con_close(void) +{ + opal_console_flush(opal_con_id); +} + +static void opal_init(void) +{ + void *opal_node; + + opal_node = finddevice("/ibm,opal"); + if (!opal_node) + return; + if (getprop(opal_node, "opal-base-address", &opal.base, sizeof(u64)) < 0) + return; + opal.base = be64_to_cpu(opal.base); + if (getprop(opal_node, "opal-entry-address", &opal.entry, sizeof(u64)) < 0) + return; + opal.entry = be64_to_cpu(opal.entry); +} + +int opal_console_init(void *devp, struct serial_console_data *scdp) +{ + opal_init(); + + if (devp) { + int n = getprop(devp, "reg", &opal_con_id, sizeof(u32)); + if (n != sizeof(u32)) + return -1; + opal_con_id = be32_to_cpu(opal_con_id); + } else + opal_con_id = 0; + + scdp->open = opal_con_open; + scdp->putc = opal_con_putc; + scdp->close = opal_con_close; + + return 0; +} -- cgit v1.3.1