* [PATCH v2 0/2] optimise blk_try_enter_queue() @ 2021-10-21 13:30 Pavel Begunkov 2021-10-21 13:30 ` [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU Pavel Begunkov ` (2 more replies) 0 siblings, 3 replies; 7+ messages in thread From: Pavel Begunkov @ 2021-10-21 13:30 UTC (permalink / raw) To: linux-block Cc: Jens Axboe, linux-kernel, linux-mm, Christoph Lameter, Tejun Heo, Dennis Zhou, Pavel Begunkov Kill extra rcu_read_lock/unlock() pair in blk_try_enter_queue(). Testing with io_uring (high batching) with nullblk: Before: 3.20% io_uring [kernel.vmlinux] [k] __rcu_read_unlock 3.05% io_uring [kernel.vmlinux] [k] __rcu_read_lock After: 2.52% io_uring [kernel.vmlinux] [k] __rcu_read_unlock 2.28% io_uring [kernel.vmlinux] [k] __rcu_read_lock Doesn't necessarily translates into 1.4% perfofrmance improvement but nice to have. v2: rcu_read_lock_held() warning (Tejun) Pavel Begunkov (2): percpu_ref: percpu_ref_tryget_live() version holding RCU block: kill extra rcu lock/unlock in queue enter block/blk-core.c | 2 +- include/linux/percpu-refcount.h | 33 +++++++++++++++++++++++---------- 2 files changed, 24 insertions(+), 11 deletions(-) -- 2.33.1 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU 2021-10-21 13:30 [PATCH v2 0/2] optimise blk_try_enter_queue() Pavel Begunkov @ 2021-10-21 13:30 ` Pavel Begunkov 2021-10-21 14:01 ` Dennis Zhou 2021-10-21 13:30 ` [PATCH v2 2/2] block: kill extra rcu lock/unlock in queue enter Pavel Begunkov 2021-10-21 14:37 ` [PATCH v2 0/2] optimise blk_try_enter_queue() Jens Axboe 2 siblings, 1 reply; 7+ messages in thread From: Pavel Begunkov @ 2021-10-21 13:30 UTC (permalink / raw) To: linux-block Cc: Jens Axboe, linux-kernel, linux-mm, Christoph Lameter, Tejun Heo, Dennis Zhou, Pavel Begunkov Add percpu_ref_tryget_live_rcu(), which is a version of percpu_ref_tryget_live() but the user is responsible for enclosing it in a RCU read lock section. Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- include/linux/percpu-refcount.h | 33 +++++++++++++++++++++++---------- 1 file changed, 23 insertions(+), 10 deletions(-) diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index ae16a9856305..b31d3f3312ce 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -266,6 +266,28 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) return percpu_ref_tryget_many(ref, 1); } +/** + * percpu_ref_tryget_live_rcu - same as percpu_ref_tryget_live() but the + * caller is responsible for taking RCU. + * + * This function is safe to call as long as @ref is between init and exit. + */ +static inline bool percpu_ref_tryget_live_rcu(struct percpu_ref *ref) +{ + unsigned long __percpu *percpu_count; + bool ret = false; + + WARN_ON_ONCE(!rcu_read_lock_held()); + + if (likely(__ref_is_percpu(ref, &percpu_count))) { + this_cpu_inc(*percpu_count); + ret = true; + } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) { + ret = atomic_long_inc_not_zero(&ref->data->count); + } + return ret; +} + /** * percpu_ref_tryget_live - try to increment a live percpu refcount * @ref: percpu_ref to try-get @@ -283,20 +305,11 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) */ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref) { - unsigned long __percpu *percpu_count; bool ret = false; rcu_read_lock(); - - if (__ref_is_percpu(ref, &percpu_count)) { - this_cpu_inc(*percpu_count); - ret = true; - } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) { - ret = atomic_long_inc_not_zero(&ref->data->count); - } - + ret = percpu_ref_tryget_live_rcu(ref); rcu_read_unlock(); - return ret; } -- 2.33.1 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU 2021-10-21 13:30 ` [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU Pavel Begunkov @ 2021-10-21 14:01 ` Dennis Zhou 2021-10-22 9:22 ` Pavel Begunkov 0 siblings, 1 reply; 7+ messages in thread From: Dennis Zhou @ 2021-10-21 14:01 UTC (permalink / raw) To: Pavel Begunkov Cc: linux-block, Jens Axboe, linux-kernel, linux-mm, Christoph Lameter, Tejun Heo Hello, On Thu, Oct 21, 2021 at 02:30:51PM +0100, Pavel Begunkov wrote: > Add percpu_ref_tryget_live_rcu(), which is a version of > percpu_ref_tryget_live() but the user is responsible for enclosing it in > a RCU read lock section. > > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > --- > include/linux/percpu-refcount.h | 33 +++++++++++++++++++++++---------- > 1 file changed, 23 insertions(+), 10 deletions(-) > > diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h > index ae16a9856305..b31d3f3312ce 100644 > --- a/include/linux/percpu-refcount.h > +++ b/include/linux/percpu-refcount.h > @@ -266,6 +266,28 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) > return percpu_ref_tryget_many(ref, 1); > } > > +/** > + * percpu_ref_tryget_live_rcu - same as percpu_ref_tryget_live() but the > + * caller is responsible for taking RCU. > + * > + * This function is safe to call as long as @ref is between init and exit. > + */ > +static inline bool percpu_ref_tryget_live_rcu(struct percpu_ref *ref) > +{ > + unsigned long __percpu *percpu_count; > + bool ret = false; > + > + WARN_ON_ONCE(!rcu_read_lock_held()); > + > + if (likely(__ref_is_percpu(ref, &percpu_count))) { > + this_cpu_inc(*percpu_count); > + ret = true; > + } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) { > + ret = atomic_long_inc_not_zero(&ref->data->count); > + } > + return ret; > +} > + > /** > * percpu_ref_tryget_live - try to increment a live percpu refcount > * @ref: percpu_ref to try-get Nit: it's dumb convention at this point, but do you mind copying this guy up. I like consistency. > @@ -283,20 +305,11 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) > */ > static inline bool percpu_ref_tryget_live(struct percpu_ref *ref) > { > - unsigned long __percpu *percpu_count; > bool ret = false; > > rcu_read_lock(); > - > - if (__ref_is_percpu(ref, &percpu_count)) { > - this_cpu_inc(*percpu_count); > - ret = true; > - } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) { > - ret = atomic_long_inc_not_zero(&ref->data->count); > - } > - > + ret = percpu_ref_tryget_live_rcu(ref); > rcu_read_unlock(); > - > return ret; > } > > -- > 2.33.1 > Currently I'm not carrying anything and I don't expect any percpu_ref work to come in. Jens, feel free to pick this up. Acked-by: Dennis Zhou <dennis@kernel.org> Thanks, Dennis ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU 2021-10-21 14:01 ` Dennis Zhou @ 2021-10-22 9:22 ` Pavel Begunkov 2021-10-22 19:22 ` Dennis Zhou 0 siblings, 1 reply; 7+ messages in thread From: Pavel Begunkov @ 2021-10-22 9:22 UTC (permalink / raw) To: Dennis Zhou Cc: linux-block, Jens Axboe, linux-kernel, linux-mm, Christoph Lameter, Tejun Heo On 10/21/21 15:01, Dennis Zhou wrote: > Hello, > > On Thu, Oct 21, 2021 at 02:30:51PM +0100, Pavel Begunkov wrote: >> Add percpu_ref_tryget_live_rcu(), which is a version of >> percpu_ref_tryget_live() but the user is responsible for enclosing it in >> a RCU read lock section. >> >> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >> --- >> include/linux/percpu-refcount.h | 33 +++++++++++++++++++++++---------- >> 1 file changed, 23 insertions(+), 10 deletions(-) >> [...] >> + >> /** >> * percpu_ref_tryget_live - try to increment a live percpu refcount >> * @ref: percpu_ref to try-get > > Nit: it's dumb convention at this point, but do you mind copying this > guy up. I like consistency. Looks Jens already took it. If you still want it moved, do you mind it in a separate patch? And I'm not sure I follow where you want it to be, currently it's right before percpu_ref_tryget_live, which uses it. -- Pavel Begunkov ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU 2021-10-22 9:22 ` Pavel Begunkov @ 2021-10-22 19:22 ` Dennis Zhou 0 siblings, 0 replies; 7+ messages in thread From: Dennis Zhou @ 2021-10-22 19:22 UTC (permalink / raw) To: Pavel Begunkov Cc: Dennis Zhou, linux-block, Jens Axboe, linux-kernel, linux-mm, Christoph Lameter, Tejun Heo On Fri, Oct 22, 2021 at 10:22:30AM +0100, Pavel Begunkov wrote: > On 10/21/21 15:01, Dennis Zhou wrote: > > Hello, > > > > On Thu, Oct 21, 2021 at 02:30:51PM +0100, Pavel Begunkov wrote: > > > Add percpu_ref_tryget_live_rcu(), which is a version of > > > percpu_ref_tryget_live() but the user is responsible for enclosing it in > > > a RCU read lock section. > > > > > > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > > > --- > > > include/linux/percpu-refcount.h | 33 +++++++++++++++++++++++---------- > > > 1 file changed, 23 insertions(+), 10 deletions(-) > > > > [...] > > > + > > > /** > > > * percpu_ref_tryget_live - try to increment a live percpu refcount > > > * @ref: percpu_ref to try-get > > > > Nit: it's dumb convention at this point, but do you mind copying this > > guy up. I like consistency. > > Looks Jens already took it. If you still want it moved, do you mind > it in a separate patch? > > And I'm not sure I follow where you want it to be, currently it's > right before percpu_ref_tryget_live, which uses it. Don't worry about it. I meant the @ref comment line. Honestly it's not really useful, it's just every other header block has that convention among most of percpu related files. If I have to make any changes in the future, I'll clean it up then. Thanks, Dennis > > -- > Pavel Begunkov ^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v2 2/2] block: kill extra rcu lock/unlock in queue enter 2021-10-21 13:30 [PATCH v2 0/2] optimise blk_try_enter_queue() Pavel Begunkov 2021-10-21 13:30 ` [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU Pavel Begunkov @ 2021-10-21 13:30 ` Pavel Begunkov 2021-10-21 14:37 ` [PATCH v2 0/2] optimise blk_try_enter_queue() Jens Axboe 2 siblings, 0 replies; 7+ messages in thread From: Pavel Begunkov @ 2021-10-21 13:30 UTC (permalink / raw) To: linux-block Cc: Jens Axboe, linux-kernel, linux-mm, Christoph Lameter, Tejun Heo, Dennis Zhou, Pavel Begunkov blk_try_enter_queue() already takes rcu_read_lock/unlock, so we can avoid the second pair in percpu_ref_tryget_live(), use a newly added percpu_ref_tryget_live_rcu(). As rcu_read_lock/unlock imply barrier()s, it's pretty noticeable, especially for for !CONFIG_PREEMPT_RCU (default for some distributions), where __rcu_read_lock/unlock() are not inlined. 3.20% io_uring [kernel.vmlinux] [k] __rcu_read_unlock 3.05% io_uring [kernel.vmlinux] [k] __rcu_read_lock 2.52% io_uring [kernel.vmlinux] [k] __rcu_read_unlock 2.28% io_uring [kernel.vmlinux] [k] __rcu_read_lock Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- block/blk-core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/blk-core.c b/block/blk-core.c index 88752e51d2b6..20e76aeb50f5 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -389,7 +389,7 @@ EXPORT_SYMBOL(blk_cleanup_queue); static bool blk_try_enter_queue(struct request_queue *q, bool pm) { rcu_read_lock(); - if (!percpu_ref_tryget_live(&q->q_usage_counter)) + if (!percpu_ref_tryget_live_rcu(&q->q_usage_counter)) goto fail; /* -- 2.33.1 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2 0/2] optimise blk_try_enter_queue() 2021-10-21 13:30 [PATCH v2 0/2] optimise blk_try_enter_queue() Pavel Begunkov 2021-10-21 13:30 ` [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU Pavel Begunkov 2021-10-21 13:30 ` [PATCH v2 2/2] block: kill extra rcu lock/unlock in queue enter Pavel Begunkov @ 2021-10-21 14:37 ` Jens Axboe 2 siblings, 0 replies; 7+ messages in thread From: Jens Axboe @ 2021-10-21 14:37 UTC (permalink / raw) To: Pavel Begunkov, linux-block Cc: Dennis Zhou, Tejun Heo, linux-mm, linux-kernel, Christoph Lameter On Thu, 21 Oct 2021 14:30:50 +0100, Pavel Begunkov wrote: > Kill extra rcu_read_lock/unlock() pair in blk_try_enter_queue(). > Testing with io_uring (high batching) with nullblk: > > Before: > 3.20% io_uring [kernel.vmlinux] [k] __rcu_read_unlock > 3.05% io_uring [kernel.vmlinux] [k] __rcu_read_lock > > [...] Applied, thanks! [1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU commit: 3b13c168186c115501ee7d194460ba2f8c825155 [2/2] block: kill extra rcu lock/unlock in queue enter commit: e94f68527a35271131cdf9d3fb4eb3c2513dc3d0 Best regards, -- Jens Axboe ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-10-22 19:22 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-10-21 13:30 [PATCH v2 0/2] optimise blk_try_enter_queue() Pavel Begunkov 2021-10-21 13:30 ` [PATCH v2 1/2] percpu_ref: percpu_ref_tryget_live() version holding RCU Pavel Begunkov 2021-10-21 14:01 ` Dennis Zhou 2021-10-22 9:22 ` Pavel Begunkov 2021-10-22 19:22 ` Dennis Zhou 2021-10-21 13:30 ` [PATCH v2 2/2] block: kill extra rcu lock/unlock in queue enter Pavel Begunkov 2021-10-21 14:37 ` [PATCH v2 0/2] optimise blk_try_enter_queue() Jens Axboe
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