From: Eelco Chaudron <echaudro@redhat.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: "Xia, Chenbo" <chenbo.xia@intel.com>,
david.marchand@redhat.com, dev@dpdk.org
Subject: Re: [PATCH v3 1/4] vhost: change vhost_virtqueue access lock to a read/write one
Date: Wed, 31 May 2023 13:13:42 +0200 [thread overview]
Message-ID: <04BFE798-9FA7-4D8F-9360-266946DAD5BC@redhat.com> (raw)
In-Reply-To: <ef872a0f-8ee7-dd06-e0d0-681cffc0a44a@redhat.com>
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 <echaudro@redhat.com>
>>> Sent: Wednesday, May 17, 2023 5:09 PM
>>> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>;
>>> david.marchand@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 <echaudro@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
>>
next prev parent reply other threads:[~2023-05-31 11:13 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-17 9:08 [PATCH v3 0/4] vhost: add device op to offload the interrupt kick Eelco Chaudron
2023-05-17 9:08 ` [PATCH v3 1/4] vhost: change vhost_virtqueue access lock to a read/write one Eelco Chaudron
2023-05-17 17:33 ` Maxime Coquelin
2023-05-18 14:46 ` Eelco Chaudron
2023-05-31 6:37 ` Xia, Chenbo
2023-05-31 9:27 ` Maxime Coquelin
2023-05-31 11:13 ` Eelco Chaudron [this message]
2023-06-01 1:45 ` Xia, Chenbo
2023-05-17 9:08 ` [PATCH v3 2/4] vhost: make the guest_notifications statistic counter atomic Eelco Chaudron
2023-05-30 12:52 ` Maxime Coquelin
2023-05-31 7:03 ` Xia, Chenbo
2023-05-17 9:09 ` [PATCH v3 3/4] vhost: fix invalid call FD handling Eelco Chaudron
2023-05-30 12:54 ` Maxime Coquelin
2023-05-31 6:12 ` Xia, Chenbo
2023-05-31 9:30 ` Maxime Coquelin
2023-05-17 9:09 ` [PATCH v3 4/4] vhost: add device op to offload the interrupt kick Eelco Chaudron
2023-05-30 13:02 ` Maxime Coquelin
2023-05-30 13:16 ` Thomas Monjalon
2023-05-30 15:16 ` Maxime Coquelin
2023-05-31 6:19 ` Xia, Chenbo
2023-05-31 9:29 ` Maxime Coquelin
2023-05-31 11:21 ` Eelco Chaudron
2023-06-01 2:18 ` Xia, Chenbo
2023-06-01 8:15 ` Eelco Chaudron
2023-06-01 8:29 ` Maxime Coquelin
2023-06-01 8:49 ` Eelco Chaudron
2023-06-01 8:53 ` Maxime Coquelin
2023-05-31 11:49 ` David Marchand
2023-05-31 12:01 ` David Marchand
2023-05-31 12:48 ` Maxime Coquelin
2023-05-31 13:13 ` Eelco Chaudron
2023-05-31 14:12 ` David Marchand
2023-05-31 14:18 ` Maxime Coquelin
2023-06-01 20:00 ` [PATCH v3 0/4] " Maxime Coquelin
2023-06-02 6:20 ` Eelco Chaudron
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