[dpdk-dev] [PATCH v2] ring: guarantee ordering of cons/prod loading when doing

[Jia He]

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 at gmail.com>
>> To: Jerin Jacob <jerin.jacob at caviumnetworks.com>
>> Cc: dev at dpdk.org, olivier.matz at 6wind.com, konstantin.ananyev at intel.com,
>>   bruce.richardson at intel.com, jianbo.liu at arm.com, hemant.agrawal at nxp.com,
>>   jie2.liu at hxt-semitech.com, bing.zhao at hxt-semitech.com,
>>   jia.he at 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