| Message ID | 20240322021244.1056223-1-ming.lei@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V5] blk-mq: don't schedule block kworker on isolated CPUs | expand |
On Thu, Mar 21, 2024 at 10:13 PM Ming Lei <ming.lei@redhat.com> wrote: > > 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> > --- > V5: > - fix comment > - add one helper for document benefit > - all are suggested by Jens > V4: > - improve comment & commit log as suggested by Tim > V3: > - avoid to check invalid cpu as reported by Bart > - take current cpu(to be offline, not done yet) into account > - simplify blk_mq_hctx_has_online_cpu() > > V2: > - remove module parameter, meantime use queue map to check if > all cpus in one hctx are offline > > > 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 555ada922cf0..06cd9c8068fc 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -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> > > @@ -2168,6 +2169,15 @@ 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. > @@ -2179,7 +2189,8 @@ 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) { > @@ -3488,14 +3499,30 @@ 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) > @@ -3503,8 +3530,7 @@ 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; > > /* > @@ -3912,6 +3938,8 @@ 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. > @@ -3938,6 +3966,15 @@ 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 > */ > -- > 2.41.0 > > Reviewed-by: Ewan D. Milne <emilne@redhat.com>
On Fri, 22 Mar 2024 10:12:44 +0800, Ming Lei wrote: > 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). > > [...] Applied, thanks! [1/1] blk-mq: don't schedule block kworker on isolated CPUs commit: 5f27f3d892743312fce237958a4194859ef93d69 Best regards,
diff --git a/block/blk-mq.c b/block/blk-mq.c index 555ada922cf0..06cd9c8068fc 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -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> @@ -2168,6 +2169,15 @@ 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. @@ -2179,7 +2189,8 @@ 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) { @@ -3488,14 +3499,30 @@ 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) @@ -3503,8 +3530,7 @@ 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; /* @@ -3912,6 +3938,8 @@ 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. @@ -3938,6 +3966,15 @@ 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 */
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> --- V5: - fix comment - add one helper for document benefit - all are suggested by Jens V4: - improve comment & commit log as suggested by Tim V3: - avoid to check invalid cpu as reported by Bart - take current cpu(to be offline, not done yet) into account - simplify blk_mq_hctx_has_online_cpu() V2: - remove module parameter, meantime use queue map to check if all cpus in one hctx are offline block/blk-mq.c | 57 +++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 47 insertions(+), 10 deletions(-)