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 --- mm/dmapool_test.c | 149 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 149 insertions(+) create mode 100644 mm/dmapool_test.c (limited to 'mm/dmapool_test.c') diff --git a/mm/dmapool_test.c b/mm/dmapool_test.c new file mode 100644 index 000000000..d829d99aa --- /dev/null +++ b/mm/dmapool_test.c @@ -0,0 +1,149 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include +#include +#include + +#define NR_TESTS (100) + +struct dma_pool_pair { + dma_addr_t dma; + void *v; +}; + +struct dmapool_parms { + size_t size; + size_t align; + size_t boundary; +}; + +static const struct dmapool_parms pool_parms[] = { + { .size = 16, .align = 16, .boundary = 0 }, + { .size = 64, .align = 64, .boundary = 0 }, + { .size = 256, .align = 256, .boundary = 0 }, + { .size = 1024, .align = 1024, .boundary = 0 }, + { .size = 4096, .align = 4096, .boundary = 0 }, + { .size = 68, .align = 32, .boundary = 4096 }, +}; + +static struct dma_pool *pool; +static struct device test_dev; +static u64 dma_mask; + +static inline int nr_blocks(int size) +{ + return clamp_t(int, (PAGE_SIZE / size) * 512, 1024, 8192); +} + +static int dmapool_test_alloc(struct dma_pool_pair *p, int blocks) +{ + int i; + + for (i = 0; i < blocks; i++) { + p[i].v = dma_pool_alloc(pool, GFP_KERNEL, + &p[i].dma); + if (!p[i].v) + goto pool_fail; + } + + for (i = 0; i < blocks; i++) + dma_pool_free(pool, p[i].v, p[i].dma); + + return 0; + +pool_fail: + for (--i; i >= 0; i--) + dma_pool_free(pool, p[i].v, p[i].dma); + return -ENOMEM; +} + +static int dmapool_test_block(const struct dmapool_parms *parms) +{ + int blocks = nr_blocks(parms->size); + ktime_t start_time, end_time; + struct dma_pool_pair *p; + int i, ret; + + p = kzalloc_objs(*p, blocks); + if (!p) + return -ENOMEM; + + pool = dma_pool_create("test pool", &test_dev, parms->size, + parms->align, parms->boundary); + if (!pool) { + ret = -ENOMEM; + goto free_pairs; + } + + start_time = ktime_get(); + for (i = 0; i < NR_TESTS; i++) { + ret = dmapool_test_alloc(p, blocks); + if (ret) + goto free_pool; + if (need_resched()) + cond_resched(); + } + end_time = ktime_get(); + + printk("dmapool test: size:%-4zu align:%-4zu blocks:%-4d time:%llu\n", + parms->size, parms->align, blocks, + ktime_us_delta(end_time, start_time)); + +free_pool: + dma_pool_destroy(pool); +free_pairs: + kfree(p); + return ret; +} + +static void dmapool_test_release(struct device *dev) +{ +} + +static int dmapool_checks(void) +{ + int i, ret; + + ret = dev_set_name(&test_dev, "dmapool-test"); + if (ret) + return ret; + + ret = device_register(&test_dev); + if (ret) { + printk("%s: register failed:%d\n", __func__, ret); + goto put_device; + } + + test_dev.release = dmapool_test_release; + set_dma_ops(&test_dev, NULL); + test_dev.dma_mask = &dma_mask; + ret = dma_set_mask_and_coherent(&test_dev, DMA_BIT_MASK(64)); + if (ret) { + printk("%s: mask failed:%d\n", __func__, ret); + goto del_device; + } + + for (i = 0; i < ARRAY_SIZE(pool_parms); i++) { + ret = dmapool_test_block(&pool_parms[i]); + if (ret) + break; + } + +del_device: + device_del(&test_dev); +put_device: + put_device(&test_dev); + return ret; +} + +static void dmapool_exit(void) +{ +} + +module_init(dmapool_checks); +module_exit(dmapool_exit); +MODULE_DESCRIPTION("dma_pool timing test"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1