Hi,
The 1st patch removes memory footprint of percpu_ref in fast path
from 7 words to 2 words, since it is often used in fast path and
embedded in user struct.
The 2nd patch moves .q_usage_counter to 1st cacheline of
'request_queue'.
Simple test on null_blk shows ~2% IOPS boost on one 16cores(two threads
per core) machine, dual socket/numa.
V7:
- add comments about reason for struct split
V6:
- drop the 1st patch which adds percpu_ref_is_initialized() for MD
only, since Christoph doesn't like it
V5:
- fix memory leak on ref->data, only percpu_ref_exit() of patch 2
is modified.
V4:
- rename percpu_ref_inited as percpu_ref_is_initialized
V3:
- fix kernel oops on MD
- add patch for avoiding to use percpu-refcount internal from md
code
- pass Red Hat CKI test which is done by Veronika Kabatova
V2:
- pass 'gfp' to kzalloc() for fixing block/027 failure reported by
kernel test robot
- protect percpu_ref_is_zero() with destroying percpu-refcount by
spin lock
Ming Lei (2):
percpu_ref: reduce memory footprint of percpu_ref in fast path
block: move 'q_usage_counter' into front of 'request_queue'
drivers/infiniband/sw/rdmavt/mr.c | 2 +-
include/linux/blkdev.h | 3 +-
include/linux/percpu-refcount.h | 52 ++++++------
lib/percpu-refcount.c | 131 ++++++++++++++++++++++--------
4 files changed, 125 insertions(+), 63 deletions(-)
Cc: Veronika Kabatova <[email protected]>
Cc: Sagi Grimberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Bart Van Assche <[email protected]>
--
2.25.2
The field of 'q_usage_counter' is always fetched in fast path of every
block driver, and move it into front of 'request_queue', so it can be
fetched into 1st cacheline of 'request_queue' instance.
Tested-by: Veronika Kabatova <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Sagi Grimberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Bart Van Assche <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
---
include/linux/blkdev.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d5a3e1a4c2f7..67935b3bef6c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -397,6 +397,8 @@ struct request_queue {
struct request *last_merge;
struct elevator_queue *elevator;
+ struct percpu_ref q_usage_counter;
+
struct blk_queue_stats *stats;
struct rq_qos *rq_qos;
@@ -569,7 +571,6 @@ struct request_queue {
* percpu_ref_kill() and percpu_ref_reinit().
*/
struct mutex mq_freeze_lock;
- struct percpu_ref q_usage_counter;
struct blk_mq_tag_set *tag_set;
struct list_head tag_set_list;
--
2.25.2
'struct percpu_ref' is often embedded into one user structure, and the
instance is usually referenced in fast path, however actually only
'percpu_count_ptr' is needed in fast path.
So move other fields into one new structure of 'percpu_ref_data', and
allocate it dynamically via kzalloc(), then memory footprint of
'percpu_ref' in fast path is reduced a lot and becomes suitable to put
into hot cacheline of user structure.
Tested-by: Veronika Kabatova <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Sagi Grimberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Bart Van Assche <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
---
drivers/infiniband/sw/rdmavt/mr.c | 2 +-
include/linux/percpu-refcount.h | 52 ++++++------
lib/percpu-refcount.c | 131 ++++++++++++++++++++++--------
3 files changed, 123 insertions(+), 62 deletions(-)
diff --git a/drivers/infiniband/sw/rdmavt/mr.c b/drivers/infiniband/sw/rdmavt/mr.c
index 2f7c25fea44a..8490fdb9c91e 100644
--- a/drivers/infiniband/sw/rdmavt/mr.c
+++ b/drivers/infiniband/sw/rdmavt/mr.c
@@ -499,7 +499,7 @@ static int rvt_check_refs(struct rvt_mregion *mr, const char *t)
rvt_pr_err(rdi,
"%s timeout mr %p pd %p lkey %x refcount %ld\n",
t, mr, mr->pd, mr->lkey,
- atomic_long_read(&mr->refcount.count));
+ atomic_long_read(&mr->refcount.data->count));
rvt_get_mr(mr);
return -EBUSY;
}
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 87d8a38bdea1..16c35a728b4c 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -92,18 +92,30 @@ enum {
PERCPU_REF_ALLOW_REINIT = 1 << 2,
};
-struct percpu_ref {
+struct percpu_ref_data {
atomic_long_t count;
- /*
- * The low bit of the pointer indicates whether the ref is in percpu
- * mode; if set, then get/put will manipulate the atomic_t.
- */
- unsigned long percpu_count_ptr;
percpu_ref_func_t *release;
percpu_ref_func_t *confirm_switch;
bool force_atomic:1;
bool allow_reinit:1;
struct rcu_head rcu;
+ struct percpu_ref *ref;
+};
+
+struct percpu_ref {
+ /*
+ * The low bit of the pointer indicates whether the ref is in percpu
+ * mode; if set, then get/put will manipulate the atomic_t.
+ */
+ unsigned long percpu_count_ptr;
+
+ /*
+ * 'percpu_ref' is often embedded into user structure, and only
+ * 'percpu_count_ptr' is required in fast path, move other fields
+ * into 'percpu_ref_data', so we can reduce memory footprint in
+ * fast path.
+ */
+ struct percpu_ref_data *data;
};
int __must_check percpu_ref_init(struct percpu_ref *ref,
@@ -118,6 +130,7 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill);
void percpu_ref_resurrect(struct percpu_ref *ref);
void percpu_ref_reinit(struct percpu_ref *ref);
+bool percpu_ref_is_zero(struct percpu_ref *ref);
/**
* percpu_ref_kill - drop the initial ref
@@ -191,7 +204,7 @@ static inline void percpu_ref_get_many(struct percpu_ref *ref, unsigned long nr)
if (__ref_is_percpu(ref, &percpu_count))
this_cpu_add(*percpu_count, nr);
else
- atomic_long_add(nr, &ref->count);
+ atomic_long_add(nr, &ref->data->count);
rcu_read_unlock();
}
@@ -231,7 +244,7 @@ static inline bool percpu_ref_tryget_many(struct percpu_ref *ref,
this_cpu_add(*percpu_count, nr);
ret = true;
} else {
- ret = atomic_long_add_unless(&ref->count, nr, 0);
+ ret = atomic_long_add_unless(&ref->data->count, nr, 0);
}
rcu_read_unlock();
@@ -279,7 +292,7 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
this_cpu_inc(*percpu_count);
ret = true;
} else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) {
- ret = atomic_long_inc_not_zero(&ref->count);
+ ret = atomic_long_inc_not_zero(&ref->data->count);
}
rcu_read_unlock();
@@ -305,8 +318,8 @@ static inline void percpu_ref_put_many(struct percpu_ref *ref, unsigned long nr)
if (__ref_is_percpu(ref, &percpu_count))
this_cpu_sub(*percpu_count, nr);
- else if (unlikely(atomic_long_sub_and_test(nr, &ref->count)))
- ref->release(ref);
+ else if (unlikely(atomic_long_sub_and_test(nr, &ref->data->count)))
+ ref->data->release(ref);
rcu_read_unlock();
}
@@ -339,21 +352,4 @@ static inline bool percpu_ref_is_dying(struct percpu_ref *ref)
return ref->percpu_count_ptr & __PERCPU_REF_DEAD;
}
-/**
- * percpu_ref_is_zero - test whether a percpu refcount reached zero
- * @ref: percpu_ref to test
- *
- * Returns %true if @ref reached zero.
- *
- * This function is safe to call as long as @ref is between init and exit.
- */
-static inline bool percpu_ref_is_zero(struct percpu_ref *ref)
-{
- unsigned long __percpu *percpu_count;
-
- if (__ref_is_percpu(ref, &percpu_count))
- return false;
- return !atomic_long_read(&ref->count);
-}
-
#endif
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 0ba686b8fe57..b6350d13538a 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -4,6 +4,7 @@
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/wait.h>
+#include <linux/slab.h>
#include <linux/percpu-refcount.h>
/*
@@ -64,18 +65,25 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
__alignof__(unsigned long));
unsigned long start_count = 0;
+ struct percpu_ref_data *data;
ref->percpu_count_ptr = (unsigned long)
__alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
if (!ref->percpu_count_ptr)
return -ENOMEM;
- ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
- ref->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;
+ data = kzalloc(sizeof(*ref->data), gfp);
+ if (!data) {
+ free_percpu((void __percpu *)ref->percpu_count_ptr);
+ return -ENOMEM;
+ }
+
+ data->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
+ data->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;
if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD)) {
ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
- ref->allow_reinit = true;
+ data->allow_reinit = true;
} else {
start_count += PERCPU_COUNT_BIAS;
}
@@ -85,14 +93,28 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
else
start_count++;
- atomic_long_set(&ref->count, start_count);
+ atomic_long_set(&data->count, start_count);
- ref->release = release;
- ref->confirm_switch = NULL;
+ data->release = release;
+ data->confirm_switch = NULL;
+ data->ref = ref;
+ ref->data = data;
return 0;
}
EXPORT_SYMBOL_GPL(percpu_ref_init);
+static void __percpu_ref_exit(struct percpu_ref *ref)
+{
+ unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+
+ if (percpu_count) {
+ /* non-NULL confirm_switch indicates switching in progress */
+ WARN_ON_ONCE(ref->data->confirm_switch);
+ free_percpu(percpu_count);
+ ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
+ }
+}
+
/**
* percpu_ref_exit - undo percpu_ref_init()
* @ref: percpu_ref to exit
@@ -105,27 +127,36 @@ EXPORT_SYMBOL_GPL(percpu_ref_init);
*/
void percpu_ref_exit(struct percpu_ref *ref)
{
- unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+ struct percpu_ref_data *data = ref->data;
+ unsigned long flags;
- if (percpu_count) {
- /* non-NULL confirm_switch indicates switching in progress */
- WARN_ON_ONCE(ref->confirm_switch);
- free_percpu(percpu_count);
- ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
- }
+ __percpu_ref_exit(ref);
+
+ if (!data)
+ return;
+
+ spin_lock_irqsave(&percpu_ref_switch_lock, flags);
+ ref->percpu_count_ptr |= atomic_long_read(&ref->data->count) <<
+ __PERCPU_REF_FLAG_BITS;
+ ref->data = NULL;
+ spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
+
+ kfree(data);
}
EXPORT_SYMBOL_GPL(percpu_ref_exit);
static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
{
- struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
+ struct percpu_ref_data *data = container_of(rcu,
+ struct percpu_ref_data, rcu);
+ struct percpu_ref *ref = data->ref;
- ref->confirm_switch(ref);
- ref->confirm_switch = NULL;
+ data->confirm_switch(ref);
+ data->confirm_switch = NULL;
wake_up_all(&percpu_ref_switch_waitq);
- if (!ref->allow_reinit)
- percpu_ref_exit(ref);
+ if (!data->allow_reinit)
+ __percpu_ref_exit(ref);
/* drop ref from percpu_ref_switch_to_atomic() */
percpu_ref_put(ref);
@@ -133,7 +164,9 @@ static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
{
- struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
+ struct percpu_ref_data *data = container_of(rcu,
+ struct percpu_ref_data, rcu);
+ struct percpu_ref *ref = data->ref;
unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
unsigned long count = 0;
int cpu;
@@ -142,7 +175,7 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
count += *per_cpu_ptr(percpu_count, cpu);
pr_debug("global %lu percpu %lu\n",
- atomic_long_read(&ref->count), count);
+ atomic_long_read(&data->count), count);
/*
* It's crucial that we sum the percpu counters _before_ adding the sum
@@ -156,11 +189,11 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
* reaching 0 before we add the percpu counts. But doing it at the same
* time is equivalent and saves us atomic operations:
*/
- atomic_long_add((long)count - PERCPU_COUNT_BIAS, &ref->count);
+ atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count);
- WARN_ONCE(atomic_long_read(&ref->count) <= 0,
+ WARN_ONCE(atomic_long_read(&data->count) <= 0,
"percpu ref (%ps) <= 0 (%ld) after switching to atomic",
- ref->release, atomic_long_read(&ref->count));
+ data->release, atomic_long_read(&data->count));
/* @ref is viewed as dead on all CPUs, send out switch confirmation */
percpu_ref_call_confirm_rcu(rcu);
@@ -186,10 +219,11 @@ static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
* Non-NULL ->confirm_switch is used to indicate that switching is
* in progress. Use noop one if unspecified.
*/
- ref->confirm_switch = confirm_switch ?: percpu_ref_noop_confirm_switch;
+ ref->data->confirm_switch = confirm_switch ?:
+ percpu_ref_noop_confirm_switch;
percpu_ref_get(ref); /* put after confirmation */
- call_rcu(&ref->rcu, percpu_ref_switch_to_atomic_rcu);
+ call_rcu(&ref->data->rcu, percpu_ref_switch_to_atomic_rcu);
}
static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
@@ -202,10 +236,10 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
return;
- if (WARN_ON_ONCE(!ref->allow_reinit))
+ if (WARN_ON_ONCE(!ref->data->allow_reinit))
return;
- atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);
+ atomic_long_add(PERCPU_COUNT_BIAS, &ref->data->count);
/*
* Restore per-cpu operation. smp_store_release() is paired
@@ -223,6 +257,8 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
static void __percpu_ref_switch_mode(struct percpu_ref *ref,
percpu_ref_func_t *confirm_switch)
{
+ struct percpu_ref_data *data = ref->data;
+
lockdep_assert_held(&percpu_ref_switch_lock);
/*
@@ -230,10 +266,10 @@ static void __percpu_ref_switch_mode(struct percpu_ref *ref,
* its completion. If the caller ensures that ATOMIC switching
* isn't in progress, this function can be called from any context.
*/
- wait_event_lock_irq(percpu_ref_switch_waitq, !ref->confirm_switch,
+ wait_event_lock_irq(percpu_ref_switch_waitq, !data->confirm_switch,
percpu_ref_switch_lock);
- if (ref->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))
+ if (data->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))
__percpu_ref_switch_to_atomic(ref, confirm_switch);
else
__percpu_ref_switch_to_percpu(ref);
@@ -266,7 +302,7 @@ void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
spin_lock_irqsave(&percpu_ref_switch_lock, flags);
- ref->force_atomic = true;
+ ref->data->force_atomic = true;
__percpu_ref_switch_mode(ref, confirm_switch);
spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
@@ -284,7 +320,7 @@ EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic);
void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref)
{
percpu_ref_switch_to_atomic(ref, NULL);
- wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
+ wait_event(percpu_ref_switch_waitq, !ref->data->confirm_switch);
}
EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic_sync);
@@ -312,7 +348,7 @@ void percpu_ref_switch_to_percpu(struct percpu_ref *ref)
spin_lock_irqsave(&percpu_ref_switch_lock, flags);
- ref->force_atomic = false;
+ ref->data->force_atomic = false;
__percpu_ref_switch_mode(ref, NULL);
spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
@@ -344,7 +380,8 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
spin_lock_irqsave(&percpu_ref_switch_lock, flags);
WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,
- "%s called more than once on %ps!", __func__, ref->release);
+ "%s called more than once on %ps!", __func__,
+ ref->data->release);
ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
__percpu_ref_switch_mode(ref, confirm_kill);
@@ -354,6 +391,34 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
}
EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
+/**
+ * percpu_ref_is_zero - test whether a percpu refcount reached zero
+ * @ref: percpu_ref to test
+ *
+ * Returns %true if @ref reached zero.
+ *
+ * This function is safe to call as long as @ref is between init and exit.
+ */
+bool percpu_ref_is_zero(struct percpu_ref *ref)
+{
+ unsigned long __percpu *percpu_count;
+ unsigned long count, flags;
+
+ if (__ref_is_percpu(ref, &percpu_count))
+ return false;
+
+ /* protect us from being destroyed */
+ spin_lock_irqsave(&percpu_ref_switch_lock, flags);
+ if (ref->data)
+ count = atomic_long_read(&ref->data->count);
+ else
+ count = ref->percpu_count_ptr >> __PERCPU_REF_FLAG_BITS;
+ spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
+
+ return count == 0;
+}
+EXPORT_SYMBOL_GPL(percpu_ref_is_zero);
+
/**
* percpu_ref_reinit - re-initialize a percpu refcount
* @ref: perpcu_ref to re-initialize
--
2.25.2
On Thu, Oct 01, 2020 at 11:48:41PM +0800, Ming Lei wrote:
> 'struct percpu_ref' is often embedded into one user structure, and the
> instance is usually referenced in fast path, however actually only
> 'percpu_count_ptr' is needed in fast path.
>
> So move other fields into one new structure of 'percpu_ref_data', and
> allocate it dynamically via kzalloc(), then memory footprint of
> 'percpu_ref' in fast path is reduced a lot and becomes suitable to put
> into hot cacheline of user structure.
>
> Tested-by: Veronika Kabatova <[email protected]>
> Reviewed-by: Christoph Hellwig <[email protected]>
> Cc: Sagi Grimberg <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Cc: Jens Axboe <[email protected]>
> Cc: Bart Van Assche <[email protected]>
> Signed-off-by: Ming Lei <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Thanks.
--
tejun
On Thu, Oct 01, 2020 at 11:48:40PM +0800, Ming Lei wrote:
> Hi,
>
> The 1st patch removes memory footprint of percpu_ref in fast path
> from 7 words to 2 words, since it is often used in fast path and
> embedded in user struct.
>
> The 2nd patch moves .q_usage_counter to 1st cacheline of
> 'request_queue'.
>
> Simple test on null_blk shows ~2% IOPS boost on one 16cores(two threads
> per core) machine, dual socket/numa.
>
> V7:
> - add comments about reason for struct split
Hello Jens
Can you consider to merge the patchset in block tree if you are fine?
Thanks,
Ming
On 10/1/20 9:48 AM, Ming Lei wrote:
> Hi,
>
> The 1st patch removes memory footprint of percpu_ref in fast path
> from 7 words to 2 words, since it is often used in fast path and
> embedded in user struct.
>
> The 2nd patch moves .q_usage_counter to 1st cacheline of
> 'request_queue'.
>
> Simple test on null_blk shows ~2% IOPS boost on one 16cores(two threads
> per core) machine, dual socket/numa.
Applied, thanks.
--
Jens Axboe