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/kbuf.h | 141 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 141 insertions(+) create mode 100644 io_uring/kbuf.h (limited to 'io_uring/kbuf.h') diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h new file mode 100644 index 000000000..401773e1e --- /dev/null +++ b/io_uring/kbuf.h @@ -0,0 +1,141 @@ +// SPDX-License-Identifier: GPL-2.0 +#ifndef IOU_KBUF_H +#define IOU_KBUF_H + +#include +#include + +enum { + /* ring mapped provided buffers */ + IOBL_BUF_RING = 1, + /* buffers are consumed incrementally rather than always fully */ + IOBL_INC = 2, +}; + +struct io_buffer_list { + /* + * If the IOBL_BUF_RING flag is set, then buf_ring is used. If not, then + * these are classic provided buffers and ->buf_list is used. + */ + union { + struct list_head buf_list; + struct io_uring_buf_ring *buf_ring; + }; + /* count of classic/legacy buffers in buffer list */ + int nbufs; + + __u16 bgid; + + /* below is for ring provided buffers */ + __u16 head; + __u16 mask; + + __u16 flags; + + /* + * minimum required amount to be left to reuse an incrementally + * consumed buffer. If less than this is left at consumption time, + * buffer is done and head is incremented to the next buffer. + */ + __u32 min_left_sub_one; + + struct io_mapped_region region; +}; + +struct io_buffer { + struct list_head list; + __u64 addr; + __u32 len; + __u16 bid; + __u16 bgid; +}; + +enum { + /* can alloc a bigger vec */ + KBUF_MODE_EXPAND = 1, + /* if bigger vec allocated, free old one */ + KBUF_MODE_FREE = 2, +}; + +struct buf_sel_arg { + struct iovec *iovs; + size_t out_len; + size_t max_len; + unsigned short nr_iovs; + unsigned short mode; + unsigned short buf_group; + unsigned short partial_map; +}; + +struct io_br_sel io_buffer_select(struct io_kiocb *req, size_t *len, + unsigned buf_group, unsigned int issue_flags); +int io_buffers_select(struct io_kiocb *req, struct buf_sel_arg *arg, + struct io_br_sel *sel, unsigned int issue_flags); +int io_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg, + struct io_br_sel *sel); +void io_destroy_buffers(struct io_ring_ctx *ctx); + +int io_remove_buffers_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe); +int io_provide_buffers_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe); +int io_manage_buffers_legacy(struct io_kiocb *req, unsigned int issue_flags); + +int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg); +int io_unregister_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg); +int io_register_pbuf_status(struct io_ring_ctx *ctx, void __user *arg); + +bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags); +void io_kbuf_drop_legacy(struct io_kiocb *req); + +unsigned int __io_put_kbufs(struct io_kiocb *req, struct io_buffer_list *bl, + int len, int nbufs); +bool io_kbuf_commit(struct io_kiocb *req, + struct io_buffer_list *bl, int len, int nr); + +struct io_mapped_region *io_pbuf_get_region(struct io_ring_ctx *ctx, + unsigned int bgid); + +static inline bool io_kbuf_recycle_ring(struct io_kiocb *req, + struct io_buffer_list *bl) +{ + if (bl) { + req->flags &= ~(REQ_F_BUFFER_RING|REQ_F_BUFFERS_COMMIT); + return true; + } + return false; +} + +static inline bool io_do_buffer_select(struct io_kiocb *req) +{ + if (!(req->flags & REQ_F_BUFFER_SELECT)) + return false; + return !(req->flags & (REQ_F_BUFFER_SELECTED|REQ_F_BUFFER_RING)); +} + +static inline bool io_kbuf_recycle(struct io_kiocb *req, struct io_buffer_list *bl, + unsigned issue_flags) +{ + if (req->flags & REQ_F_BL_NO_RECYCLE) + return false; + if (req->flags & REQ_F_BUFFER_RING) + return io_kbuf_recycle_ring(req, bl); + if (req->flags & REQ_F_BUFFER_SELECTED) + return io_kbuf_recycle_legacy(req, issue_flags); + return false; +} + +static inline unsigned int io_put_kbuf(struct io_kiocb *req, int len, + struct io_buffer_list *bl) +{ + if (!(req->flags & (REQ_F_BUFFER_RING | REQ_F_BUFFER_SELECTED))) + return 0; + return __io_put_kbufs(req, bl, len, 1); +} + +static inline unsigned int io_put_kbufs(struct io_kiocb *req, int len, + struct io_buffer_list *bl, int nbufs) +{ + if (!(req->flags & (REQ_F_BUFFER_RING | REQ_F_BUFFER_SELECTED))) + return 0; + return __io_put_kbufs(req, bl, len, nbufs); +} +#endif -- cgit v1.3.1