Re: [dpdk-dev] [PATCH v2 2/3] vhost: move dirty logging cache out of the virtqueue

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 3/16/21 2:13 PM, David Marchand wrote:
> On Tue, Mar 16, 2021 at 1:42 PM Maxime Coquelin
> <maxime.coquelin@redhat.com> wrote:
>>
>> This patch moves the per-virtqueue's dirty logging cache
>> out of the virtqueue struct, by allocating it dynamically
>> only when live-migration is enabled.
>>
>> It saves 8 cachelines in vhost_virtqueue struct.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>  lib/librte_vhost/vhost.c      | 14 ++++++++++++++
>>  lib/librte_vhost/vhost.h      |  2 +-
>>  lib/librte_vhost/vhost_user.c | 25 +++++++++++++++++++++++++
>>  3 files changed, 40 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
>> index 5a7c0c6cff..c3490ce897 100644
>> --- a/lib/librte_vhost/vhost.c
>> +++ b/lib/librte_vhost/vhost.c
>> @@ -145,6 +145,10 @@ __vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq)
>>         if (unlikely(!dev->log_base))
>>                 return;
>>
>> +       /* No cache, nothing to sync */
>> +       if (unlikely(!vq->log_cache))
>> +               return;
>> +
>>         rte_atomic_thread_fence(__ATOMIC_RELEASE);
>>
>>         log_base = (unsigned long *)(uintptr_t)dev->log_base;
>> @@ -177,6 +181,14 @@ vhost_log_cache_page(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>         uint32_t offset = page / (sizeof(unsigned long) << 3);
>>         int i;
>>
>> +       if (unlikely(!vq->log_cache)) {
>> +               /* No logging cache allocated, write dirty log map directly */
>> +               rte_smp_wmb();
> 
> We try not to reintroduce full barriers (checkpatch caught this).

Agree, the rebase introduced it again silently.

> 
>> +               vhost_log_page((uint8_t *)(uintptr_t)dev->log_base, page);
>> +
>> +               return;
>> +       }
>> +
>>         for (i = 0; i < vq->log_cache_nb_elem; i++) {
>>                 struct log_cache_entry *elem = vq->log_cache + i;
>>
>> @@ -354,6 +366,8 @@ free_vq(struct virtio_net *dev, struct vhost_virtqueue *vq)
>>         }
>>         rte_free(vq->batch_copy_elems);
>>         rte_mempool_free(vq->iotlb_pool);
>> +       if (vq->log_cache)
>> +               rte_free(vq->log_cache);
> 
> No if() needed.

Yes, will fix in next revision.

> 
>>         rte_free(vq);
>>  }
>>
>> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
>> index 717f410548..3a71dfeed9 100644
>> --- a/lib/librte_vhost/vhost.h
>> +++ b/lib/librte_vhost/vhost.h
>> @@ -183,7 +183,7 @@ struct vhost_virtqueue {
>>         bool                    used_wrap_counter;
>>         bool                    avail_wrap_counter;
>>
>> -       struct log_cache_entry log_cache[VHOST_LOG_CACHE_NR];
>> +       struct log_cache_entry *log_cache;
>>         uint16_t log_cache_nb_elem;
>>
>>         rte_rwlock_t    iotlb_lock;
>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>> index a60bb945ad..0f452d6ff3 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -2022,6 +2022,11 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
>>         rte_free(vq->batch_copy_elems);
>>         vq->batch_copy_elems = NULL;
>>
>> +       if (vq->log_cache) {
>> +               rte_free(vq->log_cache);
>> +               vq->log_cache = NULL;
>> +       }
> 
> Idem.
> 
> 

Thanks,
Maxime