From: Liu Song <[email protected]>
In "sbitmap_queue_clear_batch", a batch of completed requests may be
processed at once, but "wait_cnt" is only reduced once by
"sbitmap_queue_wake_up".
In our environment, if "/sys/block/nvme0n1/nr_requests" is adjusted to
32, it is easily because no tag and then enter the waiting situation,
if continue change "nr_requests" to 1023 at this time, it will basically
fall into the situation of permanent blocking. Because there will be
"blk_freeze_queue" in "blk_mq_update_nr_requests", which will prevent
any new requests, but due to insufficient wake-up, there are tasks
waiting for wake-up, but no new wake-up opportunities will be generated
at this time, so this situation needs to be repaired.
Signed-off-by: Liu Song <[email protected]>
---
include/linux/sbitmap.h | 8 ++++++++
lib/sbitmap.c | 22 ++++++++++++++++++----
2 files changed, 26 insertions(+), 4 deletions(-)
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 8f5a86e..153382e 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -579,6 +579,14 @@ static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
/**
+ * sbitmap_queue_wake_up_batch() - Attempt to wake up waiters in batches
+ * on a &struct sbitmap_queue.
+ * @sbq: Bitmap queue to wake up.
+ * @nr: The number of attempts to wake the waiter.
+ */
+void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr);
+
+/**
* sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
* seq_file.
* @sbq: Bitmap queue to show.
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 29eb048..f2aa1da 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -600,7 +600,7 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
return NULL;
}
-static bool __sbq_wake_up(struct sbitmap_queue *sbq)
+static bool __sbq_wake_up(struct sbitmap_queue *sbq, int *nr)
{
struct sbq_wait_state *ws;
unsigned int wake_batch;
@@ -610,6 +610,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
if (!ws)
return false;
+again:
wait_cnt = atomic_dec_return(&ws->wait_cnt);
if (wait_cnt <= 0) {
int ret;
@@ -632,10 +633,14 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
if (ret == wait_cnt) {
sbq_index_atomic_inc(&sbq->wake_index);
wake_up_nr(&ws->wait, wake_batch);
- return false;
+ if (!nr || *nr <= 0)
+ return false;
}
return true;
+ } else if (nr && *nr) {
+ (*nr)--;
+ goto again;
}
return false;
@@ -643,11 +648,20 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
{
- while (__sbq_wake_up(sbq))
+ while (__sbq_wake_up(sbq, NULL))
;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
+void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr)
+{
+ int i = SBQ_WAIT_QUEUES;
+
+ while (__sbq_wake_up(sbq, &nr) && --i)
+ ;
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up_batch);
+
static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int cpu, int tag)
{
if (likely(!sb->round_robin && tag < sb->depth))
@@ -683,7 +697,7 @@ void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
atomic_long_andnot(mask, (atomic_long_t *) addr);
smp_mb__after_atomic();
- sbitmap_queue_wake_up(sbq);
+ sbitmap_queue_wake_up_batch(sbq, nr_tags);
sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
tags[nr_tags - 1] - offset);
}
--
1.8.3.1
On 2022/9/17 11:58, Hillf Danton wrote:
> On 17 Sep 2022 10:33:01 +0800 Liu Song <[email protected]> wrote:
>> @@ -632,10 +633,14 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
>> if (ret == wait_cnt) {
>> sbq_index_atomic_inc(&sbq->wake_index);
>> wake_up_nr(&ws->wait, wake_batch);
>> - return false;
>> + if (!nr || *nr <= 0)
>> + return false;
>> }
>>
>> return true;
>> + } else if (nr && *nr) {
>> + (*nr)--;
>> + goto again;
>> }
>>
>> return false;
> Hi Song,
>
> See if advancing wake_index can survive your tests.
Hi
Thanks for your suggestion, this problem not only needs to switch a wait
queue, but also needs to consume "wait_cnt" correctly.
Thanks
>
> Only for thoughts now.
>
> Hillf
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -611,6 +611,7 @@ static bool __sbq_wake_up(struct sbitmap
> if (wait_cnt <= 0) {
> int ret;
>
> + sbq_index_atomic_inc(&sbq->wake_index);
> wake_batch = READ_ONCE(sbq->wake_batch);
>
> /*
> @@ -627,7 +628,6 @@ static bool __sbq_wake_up(struct sbitmap
> */
> ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
> if (ret == wait_cnt) {
> - sbq_index_atomic_inc(&sbq->wake_index);
> wake_up_nr(&ws->wait, wake_batch);
> return false;
> }
Hi,
?? 2022/09/17 10:33, Liu Song д??:
> From: Liu Song <[email protected]>
>
> In "sbitmap_queue_clear_batch", a batch of completed requests may be
> processed at once, but "wait_cnt" is only reduced once by
> "sbitmap_queue_wake_up".
> In our environment, if "/sys/block/nvme0n1/nr_requests" is adjusted to
> 32, it is easily because no tag and then enter the waiting situation,
> if continue change "nr_requests" to 1023 at this time, it will basically
> fall into the situation of permanent blocking. Because there will be
> "blk_freeze_queue" in "blk_mq_update_nr_requests", which will prevent
> any new requests, but due to insufficient wake-up, there are tasks
> waiting for wake-up, but no new wake-up opportunities will be generated
> at this time, so this situation needs to be repaired.
>
It seems Keith already fixed this recently. Can you have a check at his
patch?
Thanks,
Kuai
> Signed-off-by: Liu Song <[email protected]>
> ---
> include/linux/sbitmap.h | 8 ++++++++
> lib/sbitmap.c | 22 ++++++++++++++++++----
> 2 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
> index 8f5a86e..153382e 100644
> --- a/include/linux/sbitmap.h
> +++ b/include/linux/sbitmap.h
> @@ -579,6 +579,14 @@ static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
> void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
>
> /**
> + * sbitmap_queue_wake_up_batch() - Attempt to wake up waiters in batches
> + * on a &struct sbitmap_queue.
> + * @sbq: Bitmap queue to wake up.
> + * @nr: The number of attempts to wake the waiter.
> + */
> +void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr);
> +
> +/**
> * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
> * seq_file.
> * @sbq: Bitmap queue to show.
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index 29eb048..f2aa1da 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -600,7 +600,7 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
> return NULL;
> }
>
> -static bool __sbq_wake_up(struct sbitmap_queue *sbq)
> +static bool __sbq_wake_up(struct sbitmap_queue *sbq, int *nr)
> {
> struct sbq_wait_state *ws;
> unsigned int wake_batch;
> @@ -610,6 +610,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
> if (!ws)
> return false;
>
> +again:
> wait_cnt = atomic_dec_return(&ws->wait_cnt);
> if (wait_cnt <= 0) {
> int ret;
> @@ -632,10 +633,14 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
> if (ret == wait_cnt) {
> sbq_index_atomic_inc(&sbq->wake_index);
> wake_up_nr(&ws->wait, wake_batch);
> - return false;
> + if (!nr || *nr <= 0)
> + return false;
> }
>
> return true;
> + } else if (nr && *nr) {
> + (*nr)--;
> + goto again;
> }
>
> return false;
> @@ -643,11 +648,20 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
>
> void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
> {
> - while (__sbq_wake_up(sbq))
> + while (__sbq_wake_up(sbq, NULL))
> ;
> }
> EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
>
> +void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr)
> +{
> + int i = SBQ_WAIT_QUEUES;
> +
> + while (__sbq_wake_up(sbq, &nr) && --i)
> + ;
> +}
> +EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up_batch);
> +
> static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int cpu, int tag)
> {
> if (likely(!sb->round_robin && tag < sb->depth))
> @@ -683,7 +697,7 @@ void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
> atomic_long_andnot(mask, (atomic_long_t *) addr);
>
> smp_mb__after_atomic();
> - sbitmap_queue_wake_up(sbq);
> + sbitmap_queue_wake_up_batch(sbq, nr_tags);
> sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
> tags[nr_tags - 1] - offset);
> }
>
在 2022/9/17 18:20, Yu Kuai 写道:
> Hi,
>
> 在 2022/09/17 10:33, Liu Song 写道:
>> From: Liu Song <[email protected]>
>>
>> In "sbitmap_queue_clear_batch", a batch of completed requests may be
>> processed at once, but "wait_cnt" is only reduced once by
>> "sbitmap_queue_wake_up".
>> In our environment, if "/sys/block/nvme0n1/nr_requests" is adjusted to
>> 32, it is easily because no tag and then enter the waiting situation,
>> if continue change "nr_requests" to 1023 at this time, it will basically
>> fall into the situation of permanent blocking. Because there will be
>> "blk_freeze_queue" in "blk_mq_update_nr_requests", which will prevent
>> any new requests, but due to insufficient wake-up, there are tasks
>> waiting for wake-up, but no new wake-up opportunities will be generated
>> at this time, so this situation needs to be repaired.
>>
>
> It seems Keith already fixed this recently. Can you have a check at his
> patch?
>
Hi
It's a bit embarrassing. My code is 6.0-rc3. Yesterday, there was a
problem with
the Tsinghua mirror station. The fetched code could not be the latest,
so I submitted it.
According to your suggestion, I checked and it has been fixed, thank you
for your suggestion.
Thanks
> Thanks,
> Kuai
>> Signed-off-by: Liu Song <[email protected]>
>> ---
>> include/linux/sbitmap.h | 8 ++++++++
>> lib/sbitmap.c | 22 ++++++++++++++++++----
>> 2 files changed, 26 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
>> index 8f5a86e..153382e 100644
>> --- a/include/linux/sbitmap.h
>> +++ b/include/linux/sbitmap.h
>> @@ -579,6 +579,14 @@ static inline struct sbq_wait_state
>> *sbq_wait_ptr(struct sbitmap_queue *sbq,
>> void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
>> /**
>> + * sbitmap_queue_wake_up_batch() - Attempt to wake up waiters in
>> batches
>> + * on a &struct sbitmap_queue.
>> + * @sbq: Bitmap queue to wake up.
>> + * @nr: The number of attempts to wake the waiter.
>> + */
>> +void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr);
>> +
>> +/**
>> * sbitmap_queue_show() - Dump &struct sbitmap_queue information to
>> a &struct
>> * seq_file.
>> * @sbq: Bitmap queue to show.
>> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
>> index 29eb048..f2aa1da 100644
>> --- a/lib/sbitmap.c
>> +++ b/lib/sbitmap.c
>> @@ -600,7 +600,7 @@ static struct sbq_wait_state *sbq_wake_ptr(struct
>> sbitmap_queue *sbq)
>> return NULL;
>> }
>> -static bool __sbq_wake_up(struct sbitmap_queue *sbq)
>> +static bool __sbq_wake_up(struct sbitmap_queue *sbq, int *nr)
>> {
>> struct sbq_wait_state *ws;
>> unsigned int wake_batch;
>> @@ -610,6 +610,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
>> if (!ws)
>> return false;
>> +again:
>> wait_cnt = atomic_dec_return(&ws->wait_cnt);
>> if (wait_cnt <= 0) {
>> int ret;
>> @@ -632,10 +633,14 @@ static bool __sbq_wake_up(struct sbitmap_queue
>> *sbq)
>> if (ret == wait_cnt) {
>> sbq_index_atomic_inc(&sbq->wake_index);
>> wake_up_nr(&ws->wait, wake_batch);
>> - return false;
>> + if (!nr || *nr <= 0)
>> + return false;
>> }
>> return true;
>> + } else if (nr && *nr) {
>> + (*nr)--;
>> + goto again;
>> }
>> return false;
>> @@ -643,11 +648,20 @@ static bool __sbq_wake_up(struct sbitmap_queue
>> *sbq)
>> void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
>> {
>> - while (__sbq_wake_up(sbq))
>> + while (__sbq_wake_up(sbq, NULL))
>> ;
>> }
>> EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
>> +void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr)
>> +{
>> + int i = SBQ_WAIT_QUEUES;
>> +
>> + while (__sbq_wake_up(sbq, &nr) && --i)
>> + ;
>> +}
>> +EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up_batch);
>> +
>> static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int
>> cpu, int tag)
>> {
>> if (likely(!sb->round_robin && tag < sb->depth))
>> @@ -683,7 +697,7 @@ void sbitmap_queue_clear_batch(struct
>> sbitmap_queue *sbq, int offset,
>> atomic_long_andnot(mask, (atomic_long_t *) addr);
>> smp_mb__after_atomic();
>> - sbitmap_queue_wake_up(sbq);
>> + sbitmap_queue_wake_up_batch(sbq, nr_tags);
>> sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
>> tags[nr_tags - 1] - offset);
>> }
>>