6.6-stable review patch. If anyone has any objections, please let me know.
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From: Ming Lei ming.lei@redhat.com
[ Upstream commit a46c27026da10a126dd870f7b65380010bd20db5 ]
Kernel parameter of `isolcpus=` or 'nohz_full=' are used to isolate CPUs for specific task, and it isn't expected to let block IO disturb these CPUs. blk-mq kworker shouldn't be scheduled on isolated CPUs. Also if isolated CPUs is run for blk-mq kworker, long block IO latency can be caused.
Kernel workqueue only respects CPU isolation for WQ_UNBOUND, for bound WQ, the responsibility is on user because CPU is specified as WQ API parameter, such as mod_delayed_work_on(cpu), queue_delayed_work_on(cpu) and queue_work_on(cpu).
So not run blk-mq kworker on isolated CPUs by removing isolated CPUs from hctx->cpumask. Meantime use queue map to check if all CPUs in this hw queue are offline instead of hctx->cpumask, this way can avoid any cost in fast IO code path, and is safe since hctx->cpumask are only used in the two cases.
Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Juri Lelli juri.lelli@redhat.com Cc: Andrew Theurer atheurer@redhat.com Cc: Joe Mario jmario@redhat.com Cc: Sebastian Jug sejug@redhat.com Cc: Frederic Weisbecker frederic@kernel.org Cc: Bart Van Assche bvanassche@acm.org Cc: Tejun Heo tj@kernel.org Tesed-by: Joe Mario jmario@redhat.com Signed-off-by: Ming Lei ming.lei@redhat.com Reviewed-by: Ewan D. Milne emilne@redhat.com Link: https://lore.kernel.org/r/20240322021244.1056223-1-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Stable-dep-of: 10845a105bbc ("blk-mq: skip CPU offline notify on unmapped hctx") Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-mq.c | 57 +++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 47 insertions(+), 10 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 01fe1e715669..a3cd5079557b 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -30,6 +30,7 @@ #include <linux/prefetch.h> #include <linux/blk-crypto.h> #include <linux/part_stat.h> +#include <linux/sched/isolation.h>
#include <trace/events/block.h>
@@ -2193,6 +2194,15 @@ static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx) return cpu; }
+/* + * ->next_cpu is always calculated from hctx->cpumask, so simply use + * it for speeding up the check + */ +static bool blk_mq_hctx_empty_cpumask(struct blk_mq_hw_ctx *hctx) +{ + return hctx->next_cpu >= nr_cpu_ids; +} + /* * It'd be great if the workqueue API had a way to pass * in a mask and had some smarts for more clever placement. @@ -2204,7 +2214,8 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) bool tried = false; int next_cpu = hctx->next_cpu;
- if (hctx->queue->nr_hw_queues == 1) + /* Switch to unbound if no allowable CPUs in this hctx */ + if (hctx->queue->nr_hw_queues == 1 || blk_mq_hctx_empty_cpumask(hctx)) return WORK_CPU_UNBOUND;
if (--hctx->next_cpu_batch <= 0) { @@ -3535,14 +3546,30 @@ static bool blk_mq_hctx_has_requests(struct blk_mq_hw_ctx *hctx) return data.has_rq; }
-static inline bool blk_mq_last_cpu_in_hctx(unsigned int cpu, - struct blk_mq_hw_ctx *hctx) +static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx, + unsigned int this_cpu) { - if (cpumask_first_and(hctx->cpumask, cpu_online_mask) != cpu) - return false; - if (cpumask_next_and(cpu, hctx->cpumask, cpu_online_mask) < nr_cpu_ids) - return false; - return true; + enum hctx_type type = hctx->type; + int cpu; + + /* + * hctx->cpumask has to rule out isolated CPUs, but userspace still + * might submit IOs on these isolated CPUs, so use the queue map to + * check if all CPUs mapped to this hctx are offline + */ + for_each_online_cpu(cpu) { + struct blk_mq_hw_ctx *h = blk_mq_map_queue_type(hctx->queue, + type, cpu); + + if (h != hctx) + continue; + + /* this hctx has at least one online CPU */ + if (this_cpu != cpu) + return true; + } + + return false; }
static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node) @@ -3551,8 +3578,7 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node) struct blk_mq_hw_ctx, cpuhp_online); int ret = 0;
- if (!cpumask_test_cpu(cpu, hctx->cpumask) || - !blk_mq_last_cpu_in_hctx(cpu, hctx)) + if (blk_mq_hctx_has_online_cpu(hctx, cpu)) return 0;
/* @@ -4045,6 +4071,8 @@ static void blk_mq_map_swqueue(struct request_queue *q) }
queue_for_each_hw_ctx(q, hctx, i) { + int cpu; + /* * If no software queues are mapped to this hardware queue, * disable it and free the request entries. @@ -4071,6 +4099,15 @@ static void blk_mq_map_swqueue(struct request_queue *q) */ sbitmap_resize(&hctx->ctx_map, hctx->nr_ctx);
+ /* + * Rule out isolated CPUs from hctx->cpumask to avoid + * running block kworker on isolated CPUs + */ + for_each_cpu(cpu, hctx->cpumask) { + if (cpu_is_isolated(cpu)) + cpumask_clear_cpu(cpu, hctx->cpumask); + } + /* * Initialize batch roundrobin counts */