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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
References: <1509612210-5499-1-git-send-email-hejianet@gmail.com>
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<7b7f3677-8313-9a2f-868f-b3a6231548d6@gmail.com>
<20171107043655.GA3244@jerin>
<c2ce8774-a1b6-edf6-444e-ee0981df7497@gmail.com>
<20171107095727.GA23010@jerin>
From: Jia He <hejianet@gmail.com>
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Date: Wed, 8 Nov 2017 10:31:32 +0800
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Subject: Re: [dpdk-dev] [PATCH v2] ring: guarantee ordering of cons/prod
loading when doing
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Hi Jerin
Thank you,
I mistakenly think x86 doen't need rte_smp_rmb().
Since rte_smp_rmb() only impact x86's compiler optimization, I will
simplify the codes as your suggestions
Cheers,
Jia
On 11/7/2017 5:57 PM, Jerin Jacob Wrote:
> -----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.
--
Cheers,
Jia