Kernel parameter of `isolcpus=` or 'nohz_full=' are used for isolating CPUs
for specific task, and user often won't want block IO to disturb these CPUs,
also long IO latency may be caused if blk-mq kworker is scheduled on these
isolated CPUs.
Kernel workqueue only respects this limit for WQ_UNBOUND, for bound wq,
the responsibility should be on wq user.
So don't not run block kworker on isolated CPUs by ruling out isolated CPUs
from hctx->cpumask. Meantime in cpuhp handler, use queue map to check if
all CPUs in this hw queue are offline, this way can avoid any cost in fast
IO code path.
Cc: Juri Lelli <[email protected]>
Cc: Andrew Theurer <[email protected]>
Cc: Joe Mario <[email protected]>
Cc: Sebastian Jug <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
---
V2:
- remove module parameter, meantime use queue map to check if
all cpus in one hctx are offline
block/blk-mq.c | 42 +++++++++++++++++++++++++++++++++---------
1 file changed, 33 insertions(+), 9 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ec922c6bccbe..91055bdc4426 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -29,6 +29,7 @@
#include <linux/prefetch.h>
#include <linux/blk-crypto.h>
#include <linux/part_stat.h>
+#include <linux/sched/isolation.h>
#include <trace/events/block.h>
@@ -3476,14 +3477,27 @@ 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)
{
- 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;
+ struct blk_mq_tag_set *tag_set = hctx->queue->tag_set;
+ int cpu;
+
+ /*
+ * hctx->cpumask has rule out isolated CPUs, but userspace still
+ * might submit IOs on these isolated CPUs, so use queue map to
+ * check if all CPUs mapped to this hctx are offline
+ */
+ for_each_possible_cpu(cpu) {
+ unsigned idx = tag_set->map[hctx->type].mq_map[cpu];
+
+ if (idx != hctx->queue_num)
+ continue;
+
+ if (cpu_online(cpu))
+ return true;
+ }
+
+ return false;
}
static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
@@ -3491,8 +3505,7 @@ 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))
return 0;
/*
@@ -3900,6 +3913,8 @@ 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.
@@ -3926,6 +3941,15 @@ 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 for avoiding to
+ * run wq worker on isolated CPU
+ */
+ for_each_cpu(cpu, hctx->cpumask) {
+ if (cpu_is_isolated(cpu))
+ cpumask_clear_cpu(cpu, hctx->cpumask);
+ }
+
/*
* Initialize batch roundrobin counts
*/
--
2.41.0
Tested-by: Joe Mario <[email protected]>
Verified that block kworker threads no longer ran on isolated cpus.
Joe
On 10/13/23 8:47 AM, Ming Lei wrote:
> Kernel parameter of `isolcpus=` or 'nohz_full=' are used for isolating CPUs
> for specific task, and user often won't want block IO to disturb these CPUs,
> also long IO latency may be caused if blk-mq kworker is scheduled on these
> isolated CPUs.
>
> Kernel workqueue only respects this limit for WQ_UNBOUND, for bound wq,
> the responsibility should be on wq user.
>
> So don't not run block kworker on isolated CPUs by ruling out isolated CPUs
> from hctx->cpumask. Meantime in cpuhp handler, use queue map to check if
> all CPUs in this hw queue are offline, this way can avoid any cost in fast
> IO code path.
>
> Cc: Juri Lelli <[email protected]>
> Cc: Andrew Theurer <[email protected]>
> Cc: Joe Mario <[email protected]>
> Cc: Sebastian Jug <[email protected]>
> Cc: Frederic Weisbecker <[email protected]>
> Signed-off-by: Ming Lei <[email protected]>
> ---
> V2:
> - remove module parameter, meantime use queue map to check if
> all cpus in one hctx are offline
>
> block/blk-mq.c | 42 +++++++++++++++++++++++++++++++++---------
> 1 file changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index ec922c6bccbe..91055bdc4426 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -29,6 +29,7 @@
> #include <linux/prefetch.h>
> #include <linux/blk-crypto.h>
> #include <linux/part_stat.h>
> +#include <linux/sched/isolation.h>
>
> #include <trace/events/block.h>
>
> @@ -3476,14 +3477,27 @@ 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)
> {
> - 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;
> + struct blk_mq_tag_set *tag_set = hctx->queue->tag_set;
> + int cpu;
> +
> + /*
> + * hctx->cpumask has rule out isolated CPUs, but userspace still
> + * might submit IOs on these isolated CPUs, so use queue map to
> + * check if all CPUs mapped to this hctx are offline
> + */
> + for_each_possible_cpu(cpu) {
> + unsigned idx = tag_set->map[hctx->type].mq_map[cpu];
> +
> + if (idx != hctx->queue_num)
> + continue;
> +
> + if (cpu_online(cpu))
> + return true;
> + }
> +
> + return false;
> }
>
> static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
> @@ -3491,8 +3505,7 @@ 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))
> return 0;
>
> /*
> @@ -3900,6 +3913,8 @@ 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.
> @@ -3926,6 +3941,15 @@ 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 for avoiding to
> + * run wq worker on isolated CPU
> + */
> + for_each_cpu(cpu, hctx->cpumask) {
> + if (cpu_is_isolated(cpu))
> + cpumask_clear_cpu(cpu, hctx->cpumask);
> + }
> +
> /*
> * Initialize batch roundrobin counts
> */
On Fri, Oct 13, 2023 at 08:47:58PM +0800, Ming Lei wrote:
> Kernel parameter of `isolcpus=` or 'nohz_full=' are used for isolating CPUs
> for specific task, and user often won't want block IO to disturb these CPUs,
> also long IO latency may be caused if blk-mq kworker is scheduled on these
> isolated CPUs.
>
> Kernel workqueue only respects this limit for WQ_UNBOUND, for bound wq,
> the responsibility should be on wq user.
>
> So don't not run block kworker on isolated CPUs by ruling out isolated CPUs
> from hctx->cpumask. Meantime in cpuhp handler, use queue map to check if
> all CPUs in this hw queue are offline, this way can avoid any cost in fast
> IO code path.
>
> Cc: Juri Lelli <[email protected]>
> Cc: Andrew Theurer <[email protected]>
> Cc: Joe Mario <[email protected]>
> Cc: Sebastian Jug <[email protected]>
> Cc: Frederic Weisbecker <[email protected]>
> Signed-off-by: Ming Lei <[email protected]>
> ---
> V2:
> - remove module parameter, meantime use queue map to check if
> all cpus in one hctx are offline
Hello Guys,
Ping...
Thanks,
Ming
On 10/13/23 05:47, Ming Lei wrote:
> @@ -3926,6 +3941,15 @@ 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 for avoiding to
> + * run wq worker on isolated CPU
> + */
> + for_each_cpu(cpu, hctx->cpumask) {
> + if (cpu_is_isolated(cpu))
> + cpumask_clear_cpu(cpu, hctx->cpumask);
> + }
What will happen if this code makes hctx->cpumask empty? Code like
blk_mq_first_mapped_cpu() and blk_mq_hctx_next_cpu() assumes that
hctx->cpumask is not empty. There may be other code that assumes that
hctx->cpumask is not empty.
Thanks,
Bart.
On Tue, Oct 24, 2023 at 09:53:49AM -0700, Bart Van Assche wrote:
>
> On 10/13/23 05:47, Ming Lei wrote:
> > @@ -3926,6 +3941,15 @@ 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 for avoiding to
> > + * run wq worker on isolated CPU
> > + */
> > + for_each_cpu(cpu, hctx->cpumask) {
> > + if (cpu_is_isolated(cpu))
> > + cpumask_clear_cpu(cpu, hctx->cpumask);
> > + }
>
> What will happen if this code makes hctx->cpumask empty? Code like
> blk_mq_first_mapped_cpu() and blk_mq_hctx_next_cpu() assumes that
> hctx->cpumask is not empty. There may be other code that assumes that
> hctx->cpumask is not empty.
hctx->cpumask is only used for selecting next cpu to schedule run
queue now, so it is fine for hctx->cpumask to be empty.
But the patch has one hole, following the delta fix:
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0917f8eabab9..1d9a7ded27af 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2159,7 +2159,7 @@ 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)
+ if (hctx->queue->nr_hw_queues == 1 || next_cpu >= nr_cpu_ids)
return WORK_CPU_UNBOUND;
if (--hctx->next_cpu_batch <= 0) {
Thanks,
Ming