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

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

Hi Chenbo,

On 1/8/21 8:20 AM, Xia, Chenbo wrote:
> Hi Maxime,
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Tuesday, December 22, 2020 9:57 PM
>> To: dev@dpdk.org; Xia, Chenbo <chenbo.xia@intel.com>; amorenoz@redhat.com
>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Subject: [PATCH 2/3] vhost: move dirty logging cache out of the virtqueue
>>
>> 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      | 12 ++++++++++++
>>  lib/librte_vhost/vhost.h      |  2 +-
>>  lib/librte_vhost/vhost_user.c | 25 +++++++++++++++++++++++++
>>  3 files changed, 38 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
>> index 4e5df862aa..ec6459b2d1 100644
>> --- a/lib/librte_vhost/vhost.c
>> +++ b/lib/librte_vhost/vhost.c
>> @@ -144,6 +144,10 @@ __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_smp_wmb();
>>
>>  	log_base = (unsigned long *)(uintptr_t)dev->log_base;
>> @@ -176,6 +180,14 @@ 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();
>> +		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;
>>
>> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
>> index d132e4ae54..e2f14034b4 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 45c8ac09da..7ac3963a07 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -1978,6 +1978,11 @@ 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;
>> +	}
>> +
> 
> I think we'd better check and free the log cache in function free_vq() too?
> It is possible that during migration, vhost destroys, right?

Correct, I will do it too in free_vq().

Thanks!
Maxime

> Thanks,
> Chenbo
> 
>>  	msg->size = sizeof(msg->payload.state);
>>  	msg->fd_num = 0;
>>
>> @@ -2077,6 +2082,7 @@ vhost_user_set_log_base(struct virtio_net **pdev, struct
>> VhostUserMsg *msg,
>>  	int fd = msg->fds[0];
>>  	uint64_t size, off;
>>  	void *addr;
>> +	uint32_t i;
>>
>>  	if (validate_msg_fds(msg, 1) != 0)
>>  		return RTE_VHOST_MSG_RESULT_ERR;
>> @@ -2130,6 +2136,25 @@ vhost_user_set_log_base(struct virtio_net **pdev,
>> struct VhostUserMsg *msg,
>>  	dev->log_base = dev->log_addr + off;
>>  	dev->log_size = size;
>>
>> +	for (i = 0; i < dev->nr_vring; i++) {
>> +		struct vhost_virtqueue *vq = dev->virtqueue[i];
>> +
>> +		if (vq->log_cache) {
>> +			rte_free(vq->log_cache);
>> +			vq->log_cache = NULL;
>> +		}
>> +		vq->log_cache_nb_elem = 0;
>> +		vq->log_cache = rte_zmalloc("vq log cache",
>> +				sizeof(struct log_cache_entry) * VHOST_LOG_CACHE_NR,
>> +				0);
>> +		/*
>> +		 * If log cache alloc fail, don't fail migration, but no
>> +		 * caching will be done, which will impact performance
>> +		 */
>> +		if (!vq->log_cache)
>> +			VHOST_LOG_CONFIG(ERR, "Failed to allocate VQ logging
>> cache\n");
>> +	}
>> +
>>  	/*
>>  	 * The spec is not clear about it (yet), but QEMU doesn't expect
>>  	 * any payload in the reply.
>> --
>> 2.29.2
>