[dpdk-dev] [PATCH 2/4] vhost: introduce vhost_log_write

[Xie, Huawei]

On 12/2/2015 9:53 PM, Victor Kaplansky wrote:
> On Wed, Dec 02, 2015 at 11:43:11AM +0800, Yuanhan Liu wrote:
>> Introduce vhost_log_write() helper function to log the dirty pages we
>> touched. Page size is harded code to 4096 (VHOST_LOG_PAGE), and each
>> log is presented by 1 bit.
>>
>> Therefore, vhost_log_write() simply finds the right bit for related
>> page we are gonna change, and set it to 1. dev->log_base denotes the
>> start of the dirty page bitmap.
>>
>> The page address is biased by log_guest_addr, which is derived from
>> SET_VRING_ADDR request as part of the vring related addresses.
>>
>> Signed-off-by: Yuanhan Liu <yuanhan.liu at linux.intel.com>
>> ---
>>  lib/librte_vhost/rte_virtio_net.h | 34 ++++++++++++++++++++++++++++++++++
>>  lib/librte_vhost/virtio-net.c     |  4 ++++
>>  2 files changed, 38 insertions(+)
>>
>> diff --git a/lib/librte_vhost/rte_virtio_net.h b/lib/librte_vhost/rte_virtio_net.h
>> index 416dac2..191c1be 100644
>> --- a/lib/librte_vhost/rte_virtio_net.h
>> +++ b/lib/librte_vhost/rte_virtio_net.h
>> @@ -40,6 +40,7 @@
>>   */
>>  
>>  #include <stdint.h>
>> +#include <linux/vhost.h>
>>  #include <linux/virtio_ring.h>
>>  #include <linux/virtio_net.h>
>>  #include <sys/eventfd.h>
>> @@ -59,6 +60,8 @@ struct rte_mbuf;
>>  /* Backend value set by guest. */
>>  #define VIRTIO_DEV_STOPPED -1
>>  
>> +#define VHOST_LOG_PAGE	4096
>> +
>>  
>>  /* Enum for virtqueue management. */
>>  enum {VIRTIO_RXQ, VIRTIO_TXQ, VIRTIO_QNUM};
>> @@ -82,6 +85,7 @@ struct vhost_virtqueue {
>>  	struct vring_desc	*desc;			/**< Virtqueue descriptor ring. */
>>  	struct vring_avail	*avail;			/**< Virtqueue available ring. */
>>  	struct vring_used	*used;			/**< Virtqueue used ring. */
>> +	uint64_t		log_guest_addr;		/**< Physical address of used ring, for logging */
>>  	uint32_t		size;			/**< Size of descriptor ring. */
>>  	uint32_t		backend;		/**< Backend value to determine if device should started/stopped. */
>>  	uint16_t		vhost_hlen;		/**< Vhost header length (varies depending on RX merge buffers. */
>> @@ -203,6 +207,36 @@ gpa_to_vva(struct virtio_net *dev, uint64_t guest_pa)
>>  	return vhost_va;
>>  }
>>  
>> +static inline void __attribute__((always_inline))
>> +vhost_log_page(uint8_t *log_base, uint64_t page)
>> +{
>> +	/* TODO: to make it atomic? */
>> +	log_base[page / 8] |= 1 << (page % 8);
> I think the atomic OR operation is necessary only if there can be
> more than one vhost-user back-end updating the guest's memory
> simultaneously. However probably it is pretty safe to perform
> regular OR operation, since rings are not shared between
> back-end. What about buffers pointed by descriptors?  To be on
> the safe side, I would use a GCC built-in function
> __sync_fetch_and_or(). 
>
>> +}
>> +
>> +static inline void __attribute__((always_inline))
>> +vhost_log_write(struct virtio_net *dev, struct vhost_virtqueue *vq,
>> +		uint64_t offset, uint64_t len)
>> +{
>> +	uint64_t addr = vq->log_guest_addr;
>> +	uint64_t page;
>> +
>> +	if (unlikely(((dev->features & (1ULL << VHOST_F_LOG_ALL)) == 0) ||
>> +		     !dev->log_base || !len))
>> +		return;
> Isn't "likely" more appropriate in above, since the whole
> expression is expected to be true most of the time?
Victor:
So we are not always logging, what is the message that tells the backend
the migration is started?
[...]