On 31 May 2023, at 11:27, Maxime Coquelin wrote:
> On 5/31/23 08:37, Xia, Chenbo wrote:
>> Hi Eelco,
>>
>>> -----Original Message-----
>>> From: Eelco Chaudron <echau...@redhat.com>
>>> Sent: Wednesday, May 17, 2023 5:09 PM
>>> To: maxime.coque...@redhat.com; Xia, Chenbo <chenbo....@intel.com>;
>>> david.march...@redhat.com
>>> Cc: dev@dpdk.org
>>> Subject: [PATCH v3 1/4] vhost: change vhost_virtqueue access lock to a
>>> read/write one
>>>
>>> This change will allow the vhost interrupt datapath handling to be split
>>> between two processed without one of them holding an explicit lock.
>>>
>>> Signed-off-by: Eelco Chaudron <echau...@redhat.com>
>>> ---
>>> lib/eal/include/generic/rte_rwlock.h | 17 ++++++
>>> lib/vhost/vhost.c | 46 +++++++++--------
>>> lib/vhost/vhost.h | 4 +-
>>> lib/vhost/vhost_user.c | 14 +++--
>>> lib/vhost/virtio_net.c | 90 +++++++++++++++++------------
>>> -----
>>> 5 files changed, 94 insertions(+), 77 deletions(-)
>>>
>>> diff --git a/lib/eal/include/generic/rte_rwlock.h
>>> b/lib/eal/include/generic/rte_rwlock.h
>>> index 71e2d8d5f4..9e083bbc61 100644
>>> --- a/lib/eal/include/generic/rte_rwlock.h
>>> +++ b/lib/eal/include/generic/rte_rwlock.h
>>> @@ -236,6 +236,23 @@ rte_rwlock_write_unlock(rte_rwlock_t *rwl)
>>> __atomic_fetch_sub(&rwl->cnt, RTE_RWLOCK_WRITE, __ATOMIC_RELEASE);
>>> }
>>>
>>> +/**
>>> + * Test if the write lock is taken.
>>> + *
>>> + * @param rwl
>>> + * A pointer to a rwlock structure.
>>> + * @return
>>> + * 1 if the write lock is currently taken; 0 otherwise.
>>> + */
>>> +static inline int
>>> +rte_rwlock_write_is_locked(rte_rwlock_t *rwl)
>>> +{
>>> + if (__atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED) & RTE_RWLOCK_WRITE)
>>> + return 1;
>>> +
>>> + return 0;
>>> +}
>>> +
>>
>> Again we need to update release note as it's a new EAL API.
>>
>>> /**
>>> * Try to execute critical section in a hardware memory transaction, if
>>> it
>>> * fails or not available take a read lock
>>> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
>>> index ef37943817..74bdbfd810 100644
>>> --- a/lib/vhost/vhost.c
>>> +++ b/lib/vhost/vhost.c
>>> @@ -393,9 +393,9 @@ free_vq(struct virtio_net *dev, struct vhost_virtqueue
>>> *vq)
>>> else
>>> rte_free(vq->shadow_used_split);
>>>
>>> - rte_spinlock_lock(&vq->access_lock);
>>> + rte_rwlock_write_lock(&vq->access_lock);
>>> vhost_free_async_mem(vq);
>>> - rte_spinlock_unlock(&vq->access_lock);
>>> + rte_rwlock_write_unlock(&vq->access_lock);
>>> rte_free(vq->batch_copy_elems);
>>> vhost_user_iotlb_destroy(vq);
>>> rte_free(vq->log_cache);
>>> @@ -630,7 +630,7 @@ alloc_vring_queue(struct virtio_net *dev, uint32_t
>>> vring_idx)
>>>
>>> dev->virtqueue[i] = vq;
>>> init_vring_queue(dev, vq, i);
>>> - rte_spinlock_init(&vq->access_lock);
>>> + rte_rwlock_init(&vq->access_lock);
>>> vq->avail_wrap_counter = 1;
>>> vq->used_wrap_counter = 1;
>>> vq->signalled_used_valid = false;
>>> @@ -1305,14 +1305,14 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
>>> if (!vq)
>>> return -1;
>>>
>>> - rte_spinlock_lock(&vq->access_lock);
>>> + rte_rwlock_read_lock(&vq->access_lock);
>>>
>>> if (vq_is_packed(dev))
>>> vhost_vring_call_packed(dev, vq);
>>> else
>>> vhost_vring_call_split(dev, vq);
>>>
>>> - rte_spinlock_unlock(&vq->access_lock);
>>> + rte_rwlock_read_unlock(&vq->access_lock);
>>
>> Not sure about this. vhost_ring_call_packed/split is changing some field in
>> Vq. Should we use write lock here?
>
> I don't think so, the purpose of the access_lock is not to make the
> datapath threads-safe, but to protect the datapath from metadata changes
> by the control path.
Thanks Chinbo for the review, and see Maxime’s comment above. Does this clarify
your concern/question?
>>
>> Thanks,
>> Chenbo
>>
