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

[Maxime Coquelin]

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.coque...@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;
+       }
+
        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