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 --- io_uring/opdef.h | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 58 insertions(+) create mode 100644 io_uring/opdef.h (limited to 'io_uring/opdef.h') diff --git a/io_uring/opdef.h b/io_uring/opdef.h new file mode 100644 index 000000000..667f981e6 --- /dev/null +++ b/io_uring/opdef.h @@ -0,0 +1,58 @@ +// SPDX-License-Identifier: GPL-2.0 +#ifndef IOU_OP_DEF_H +#define IOU_OP_DEF_H + +struct io_uring_bpf_ctx; + +struct io_issue_def { + /* needs req->file assigned */ + unsigned needs_file : 1; + /* should block plug */ + unsigned plug : 1; + /* supports ioprio */ + unsigned ioprio : 1; + /* supports iopoll */ + unsigned iopoll : 1; + /* op supports buffer selection */ + unsigned buffer_select : 1; + /* hash wq insertion if file is a regular file */ + unsigned hash_reg_file : 1; + /* unbound wq insertion if file is a non-regular file */ + unsigned unbound_nonreg_file : 1; + /* set if opcode supports polled "wait" */ + unsigned pollin : 1; + unsigned pollout : 1; + unsigned poll_exclusive : 1; + /* skip auditing */ + unsigned audit_skip : 1; + /* vectored opcode, set if 1) vectored, and 2) handler needs to know */ + unsigned vectored : 1; + /* set to 1 if this opcode uses 128b sqes in a mixed sq */ + unsigned is_128 : 1; + + /* size of async data needed, if any */ + unsigned short async_size; + + /* bpf filter pdu size, if any */ + unsigned short filter_pdu_size; + + int (*issue)(struct io_kiocb *, unsigned int); + int (*prep)(struct io_kiocb *, const struct io_uring_sqe *); + void (*filter_populate)(struct io_uring_bpf_ctx *, struct io_kiocb *); +}; + +struct io_cold_def { + const char *name; + + void (*sqe_copy)(struct io_kiocb *); + void (*cleanup)(struct io_kiocb *); + void (*fail)(struct io_kiocb *); +}; + +extern const struct io_issue_def io_issue_defs[]; +extern const struct io_cold_def io_cold_defs[]; + +bool io_uring_op_supported(u8 opcode); + +void io_uring_optable_init(void); +#endif -- cgit v1.3.1