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blk-mq: don't schedule block kworker on isolated CPUs

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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>
This commit is contained in:
Ming Lei 2024-03-22 10:12:44 +08:00 committed by Jens Axboe
parent 7d8d35791b
commit a46c27026d
1 changed files with 47 additions and 10 deletions
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57
block/blk-mq.c
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@ -28,6 +28,7 @@
#include <linux/prefetch.h>
#include <linux/blk-crypto.h>
#include <linux/part_stat.h>
#include <linux/sched/isolation.h>
#include <trace/events/block.h>
@ -2163,6 +2164,15 @@ 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.
@ -2174,7 +2184,8 @@ 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) {
@ -3483,14 +3494,30 @@ 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)
@ -3498,8 +3525,7 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
struct blk_mq_hw_ctx, cpuhp_online);
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;
/*
@ -3907,6 +3933,8 @@ 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.
@ -3933,6 +3961,15 @@ 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
*/