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From: Jerin Jacob <jerin.jacob@caviumnetworks.com>
To: Jia He <hejianet@gmail.com>
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Subject: Re: [dpdk-dev] [PATCH v2] ring: guarantee ordering of cons/prod
loading when doing
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-----Original Message-----
> Date: Tue, 7 Nov 2017 16:34:30 +0800
> From: Jia He <hejianet@gmail.com>
> To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> Cc: dev@dpdk.org, olivier.matz@6wind.com, konstantin.ananyev@intel.com,
> bruce.richardson@intel.com, jianbo.liu@arm.com, hemant.agrawal@nxp.com,
> jie2.liu@hxt-semitech.com, bing.zhao@hxt-semitech.com,
> jia.he@hxt-semitech.com
> Subject: Re: [PATCH v2] ring: guarantee ordering of cons/prod loading when
> doing
> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
> Thunderbird/52.4.0
>
>
>
> On 11/7/2017 12:36 PM, Jerin Jacob Wrote:
> > -----Original Message-----
> >
> > On option could be to change the prototype of update_tail() and make
> > compiler accommodate it for zero cost for arm64(Which I think, it it the
> > case. But you can check the generated instructions)
> > If not, move, __rte_ring_do_dequeue() and __rte_ring_do_enqueue() instead of
> > __rte_ring_move_prod_head/__rte_ring_move_cons_head/update_tail()
> >
> >
> > ➜ [master][dpdk.org] $ git diff
> > diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
> > index 5e9b3b7b4..b32648825 100644
> > --- a/lib/librte_ring/rte_ring.h
> > +++ b/lib/librte_ring/rte_ring.h
> > @@ -358,8 +358,12 @@ void rte_ring_dump(FILE *f, const struct rte_ring
> > *r);
> > static __rte_always_inline void
> > update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t
> > new_val,
> > - uint32_t single)
> > + uint32_t single, const uint32_t enqueue)
> > {
> > + if (enqueue)
> > + rte_smp_wmb();
> > + else
> > + rte_smp_rmb();
> > /*
> > * If there are other enqueues/dequeues in progress that
> > * preceded us,
> > * we need to wait for them to complete
> > @@ -470,9 +474,8 @@ __rte_ring_do_enqueue(struct rte_ring *r, void *
> > const *obj_table,
> > goto end;
> > ENQUEUE_PTRS(r, &r[1], prod_head, obj_table, n, void *);
> > - rte_smp_wmb();
> > - update_tail(&r->prod, prod_head, prod_next, is_sp);
> > + update_tail(&r->prod, prod_head, prod_next, is_sp, 1);
> > end:
> > if (free_space != NULL)
> > *free_space = free_entries - n;
> > @@ -575,9 +578,8 @@ __rte_ring_do_dequeue(struct rte_ring *r, void
> > **obj_table,
> > goto end;
> > DEQUEUE_PTRS(r, &r[1], cons_head, obj_table, n, void *);
> > - rte_smp_rmb();
> > - update_tail(&r->cons, cons_head, cons_next, is_sc);
> > + update_tail(&r->cons, cons_head, cons_next, is_sc, 0);
> > end:
> > if (available != NULL)
> >
> >
> >
> Hi Jerin, yes I knew this suggestion in update_tail.
> But what I mean is the rte_smp_rmb() in __rte_ring_move_cons_head and
> __rte_ring_move_pros_head:
> [option 1]
> + *old_head = r->cons.head;
> + rte_smp_rmb();
> + const uint32_t prod_tail = r->prod.tail;
>
> [option 2]
> + *old_head = __atomic_load_n(&r->cons.head,
> + __ATOMIC_ACQUIRE);
> + *old_head = r->cons.head;
>
> ie.I wonder what is the suitable new config name to distinguish the above 2
> options?
Why?
If you fix the generic version with rte_smp_rmb() then we just need only
one config to differentiate between c11 vs generic. See comments below,
> Thanks for the patience :-)
>
> see my drafted patch below, the marcro "PREFER":
> + */
> +
> +#ifndef _RTE_RING_C11_MEM_H_
> +#define _RTE_RING_C11_MEM_H_
> +
> +static __rte_always_inline void
> +update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t
> new_val,
> + uint32_t single, uint32_t enqueue)
> +{
> + /* Don't need wmb/rmb when we prefer to use load_acquire/
> + * store_release barrier */
> +#ifndef PREFER
> + if (enqueue)
> + rte_smp_wmb();
> + else
> + rte_smp_rmb();
> +#endif
You can remove PREFER and let the "generic" version has this. For x86,
rte_smp_?mb() it will be NOOP. So no issue.
> +
> + /*
> + * If there are other enqueues/dequeues in progress that preceded us,
> + * we need to wait for them to complete
> + */
> + if (!single)
> + while (unlikely(ht->tail != old_val))
> + rte_pause();
> +
> +#ifdef PREFER
> + __atomic_store_n(&ht->tail, new_val, __ATOMIC_RELEASE);
for c11 mem model version, it needs only __atomic_store_n version.
> +#else
> + ht->tail = new_val;
> +#endif
> +}
> +
> +/**
> + * @internal This function updates the producer head for enqueue
> + *
> + * @param r
> + * A pointer to the ring structure
> + * @param is_sp
> + * Indicates whether multi-producer path is needed or not
> + * @param n
> + * The number of elements we will want to enqueue, i.e. how far should
> the
> + * head be moved
> + * @param behavior
> + * RTE_RING_QUEUE_FIXED: Enqueue a fixed number of items from a ring
> + * RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
> + * @param old_head
> + * Returns head value as it was before the move, i.e. where enqueue
> starts
> + * @param new_head
> + * Returns the current/new head value i.e. where enqueue finishes
> + * @param free_entries
> + * Returns the amount of free space in the ring BEFORE head was moved
> + * @return
> + * Actual number of objects enqueued.
> + * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
> + */
> +static __rte_always_inline unsigned int
> +__rte_ring_move_prod_head(struct rte_ring *r, int is_sp,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + uint32_t *old_head, uint32_t *new_head,
> + uint32_t *free_entries)
> +{
> + const uint32_t capacity = r->capacity;
> + unsigned int max = n;
> + int success;
> +
> + do {
> + /* Reset n to the initial burst count */
> + n = max;
> +
> +#ifdef PREFER
> + *old_head = __atomic_load_n(&r->prod.head,
> + __ATOMIC_ACQUIRE);
> +#else
> + *old_head = r->prod.head;
> + /* prevent reorder of load/load */
> + rte_smp_rmb();
> +#endif
Same as above comment.
> + const uint32_t cons_tail = r->cons.tail;
> + /*
> + * The subtraction is done between two unsigned 32bits value
> + * (the result is always modulo 32 bits even if we have
> + * *old_head > cons_tail). So 'free_entries' is always between 0
> + * and capacity (which is < size).
> + */
> + *free_entries = (capacity + cons_tail - *old_head);
> +
> + /* check that we have enough room in ring */
> + if (unlikely(n > *free_entries))
> +static __rte_always_inline unsigned int
> +__rte_ring_do_enqueue(struct rte_ring *r, void * const *obj_table,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + int is_sp, unsigned int *free_space)
> +{
Duplicate function, No need to replicate on both versions.
> +static __rte_always_inline unsigned int
> +__rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + uint32_t *old_head, uint32_t *new_head,
> + uint32_t *entries)
> +{
> + unsigned int max = n;
> + int success;
> +
> + /* move cons.head atomically */
> + do {
> + /* Restore n as it may change every loop */
> + n = max;
> +#ifdef PREFER
> + *old_head = __atomic_load_n(&r->cons.head,
> + __ATOMIC_ACQUIRE);
> +#else
> + *old_head = r->cons.head;
> + /* prevent reorder of load/load */
> + rte_smp_rmb();
> +#endif
Same as above comment
> +
> + const uint32_t prod_tail = r->prod.tail;
> + /* The subtraction is done between two unsigned 32bits value
> + * (the result is always modulo 32 bits even if we have
> + * cons_head > prod_tail). So 'entries' is always between 0
> + * and size(ring)-1. */
> + *entries = (prod_tail - *old_head);
> +
> + /* Set the actual entries for dequeue */
> + if (n > *entries)
> + n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;
> +
> + if (unlikely(n == 0))
> + return 0;
> +
> + *new_head = *old_head + n;
> + if (is_sc)
> + r->cons.head = *new_head, success = 1;
> + else
> +#ifdef PREFER
> + success = arch_rte_atomic32_cmpset(&r->cons.head,
> + old_head, *new_head,
> + 0, __ATOMIC_ACQUIRE,
> + __ATOMIC_RELAXED);
> +#else
> + success = rte_atomic32_cmpset(&r->cons.head, *old_head,
> + *new_head);
> +#endif
Same as above comment
> + } while (unlikely(success == 0));
> + return n;
> +}
> +
> +/**
> + * @internal Dequeue several objects from the ring
> + *
> + * @param r
> + * A pointer to the ring structure.
> + * @param obj_table
> + * A pointer to a table of void * pointers (objects).
> + * @param n
> + * The number of objects to pull from the ring.
> + * @param behavior
> + * RTE_RING_QUEUE_FIXED: Dequeue a fixed number of items from a ring
> + * RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
> + * @param is_sc
> + * Indicates whether to use single consumer or multi-consumer head update
> + * @param available
> + * returns the number of remaining ring entries after the dequeue has
> finished
> + * @return
> + * - Actual number of objects dequeued.
> + * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
> + */
> +static __rte_always_inline unsigned int
> +__rte_ring_do_dequeue(struct rte_ring *r, void **obj_table,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + int is_sc, unsigned int *available)
> +{
Duplicate function, No need to replicate on both versions.
> + uint32_t cons_head, cons_next;
> + uint32_t entries;
> +
> + n = __rte_ring_move_cons_head(r, is_sc, n, behavior,
> + &cons_head, &cons_next, &entries);
> + if (n == 0)
> + goto end;
> +
> + DEQUEUE_PTRS(r, &r[1], cons_head, obj_table, n, void *);
> +
> + update_tail(&r->cons, cons_head, cons_next, is_sc, 0);
> +
> +end:
> + if (available != NULL)
> + *available = entries - n;
> + return n;
> +}
> +
> +#endif /* _RTE_RING_C11_MEM_H_ */
> +
> diff --git a/lib/librte_ring/rte_ring_generic.h
> b/lib/librte_ring/rte_ring_generic.h
> new file mode 100644
> index 0000000..0ce6d57
> --- /dev/null
> +++ b/lib/librte_ring/rte_ring_generic.h
> @@ -0,0 +1,268 @@
> +/*-
> + * BSD LICENSE
> + *
> + * Copyright(c) 2017 hxt-semitech. All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + *
> + * * Redistributions of source code must retain the above copyright
> + * notice, this list of conditions and the following disclaimer.
> + * * Redistributions in binary form must reproduce the above copyright
> + * notice, this list of conditions and the following disclaimer in
> + * the documentation and/or other materials provided with the
> + * distribution.
> + * * Neither the name of hxt-semitech nor the names of its
> + * contributors may be used to endorse or promote products derived
> + * from this software without specific prior written permission.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
> + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
> + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> + */
> +
> +#ifndef _RTE_RING_GENERIC_H_
> +#define _RTE_RING_GENERIC_H_
> +
> +static __rte_always_inline void
> +update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t
> new_val,
> + uint32_t single, uint32_t enqueue)
> +{
> + if (enqueue)
> + rte_smp_wmb();
> + else
> + rte_smp_rmb();
> + /*
> + * If there are other enqueues/dequeues in progress that preceded us,
> + * we need to wait for them to complete
> + */
> + if (!single)
> + while (unlikely(ht->tail != old_val))
> + rte_pause();
> +
> + ht->tail = new_val;
> +}
> +
> +/**
> + * @internal This function updates the producer head for enqueue
> + *
> + * @param r
> + * A pointer to the ring structure
> + * @param is_sp
> + * Indicates whether multi-producer path is needed or not
> + * @param n
> + * The number of elements we will want to enqueue, i.e. how far should
> the
> + * head be moved
> + * @param behavior
> + * RTE_RING_QUEUE_FIXED: Enqueue a fixed number of items from a ring
> + * RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
> + * @param old_head
> + * Returns head value as it was before the move, i.e. where enqueue
> starts
> + * @param new_head
> + * Returns the current/new head value i.e. where enqueue finishes
> + * @param free_entries
> + * Returns the amount of free space in the ring BEFORE head was moved
> + * @return
> + * Actual number of objects enqueued.
> + * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
> + */
> +static __rte_always_inline unsigned int
> +__rte_ring_move_prod_head(struct rte_ring *r, int is_sp,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + uint32_t *old_head, uint32_t *new_head,
> + uint32_t *free_entries)
> +{
> + const uint32_t capacity = r->capacity;
> + unsigned int max = n;
> + int success;
> +
> + do {
> + /* Reset n to the initial burst count */
> + n = max;
> +
> + *old_head = r->prod.head;
adding rte_smp_rmb() no harm here as it is NOOP for x86 and it is
semantically correct too.
> + const uint32_t cons_tail = r->cons.tail;
> + /*
> + * The subtraction is done between two unsigned 32bits value
> + * (the result is always modulo 32 bits even if we have
> + * *old_head > cons_tail). So 'free_entries' is always between 0
> + * and capacity (which is < size).
> + */
> + *free_entries = (capacity + cons_tail - *old_head);
> +
> + /* check that we have enough room in ring */
> + if (unlikely(n > *free_entries))
> + n = (behavior == RTE_RING_QUEUE_FIXED) ?
> + 0 : *free_entries;
> +
> + if (n == 0)
> + return 0;
> +
> + *new_head = *old_head + n;
> + if (is_sp)
> + r->prod.head = *new_head, success = 1;
> + else
> + success = rte_atomic32_cmpset(&r->prod.head,
> + *old_head, *new_head);
> + } while (unlikely(success == 0));
> + return n;
> +}
> +
> +/**
> + * @internal Enqueue several objects on the ring
> + *
> + * @param r
> + * A pointer to the ring structure.
> + * @param obj_table
> + * A pointer to a table of void * pointers (objects).
> + * @param n
> + * The number of objects to add in the ring from the obj_table.
> + * @param behavior
> + * RTE_RING_QUEUE_FIXED: Enqueue a fixed number of items from a ring
> + * RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
> + * @param is_sp
> + * Indicates whether to use single producer or multi-producer head update
> + * @param free_space
> + * returns the amount of space after the enqueue operation has finished
> + * @return
> + * Actual number of objects enqueued.
> + * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
> + */
> +static __rte_always_inline unsigned int
> +__rte_ring_do_enqueue(struct rte_ring *r, void * const *obj_table,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + int is_sp, unsigned int *free_space)
> +{
Duplicate function, No need to replicate on both versions.
> +
> +/**
> + * @internal This function updates the consumer head for dequeue
> + *
> + * @param r
> + * A pointer to the ring structure
> + * @param is_sc
> + * Indicates whether multi-consumer path is needed or not
> + * @param n
> + * The number of elements we will want to enqueue, i.e. how far should
> the
> + * head be moved
> + * @param behavior
> + * RTE_RING_QUEUE_FIXED: Dequeue a fixed number of items from a ring
> + * RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
> + * @param old_head
> + * Returns head value as it was before the move, i.e. where dequeue
> starts
> + * @param new_head
> + * Returns the current/new head value i.e. where dequeue finishes
> + * @param entries
> + * Returns the number of entries in the ring BEFORE head was moved
> + * @return
> + * - Actual number of objects dequeued.
> + * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
> + */
> +static __rte_always_inline unsigned int
> +__rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + uint32_t *old_head, uint32_t *new_head,
> + uint32_t *entries)
> +{
> + unsigned int max = n;
> + int success;
> +
> + /* move cons.head atomically */
> + do {
> + /* Restore n as it may change every loop */
> + n = max;
> +
> + *old_head = r->cons.head;
> + const uint32_t prod_tail = r->prod.tail;
Same as above comment.
> + /* The subtraction is done between two unsigned 32bits value
> + * (the result is always modulo 32 bits even if we have
> + * cons_head > prod_tail). So 'entries' is always between 0
> + * and size(ring)-1. */
> + *entries = (prod_tail - *old_head);
> +
> + /* Set the actual entries for dequeue */
> + if (n > *entries)
> + n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;
> +
> + if (unlikely(n == 0))
> + return 0;
> +
> + *new_head = *old_head + n;
> + if (is_sc)
> + r->cons.head = *new_head, success = 1;
> + else
> + success = rte_atomic32_cmpset(&r->cons.head, *old_head,
> + *new_head);
> + } while (unlikely(success == 0));
> + return n;
> +}
> +
> +/**
> + * @internal Dequeue several objects from the ring
> + *
> + * @param r
> + * A pointer to the ring structure.
> + * @param obj_table
> + * A pointer to a table of void * pointers (objects).
> + * @param n
> + * The number of objects to pull from the ring.
> + * @param behavior
> + * RTE_RING_QUEUE_FIXED: Dequeue a fixed number of items from a ring
> + * RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
> + * @param is_sc
> + * Indicates whether to use single consumer or multi-consumer head update
> + * @param available
> + * returns the number of remaining ring entries after the dequeue has
> finished
> + * @return
> + * - Actual number of objects dequeued.
> + * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
> + */
> +static __rte_always_inline unsigned int
> +__rte_ring_do_dequeue(struct rte_ring *r, void **obj_table,
> + unsigned int n, enum rte_ring_queue_behavior behavior,
> + int is_sc, unsigned int *available)
> +{
Duplicate function, No need to replicate on both versions.
>