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vhost: improve dirty pages logging performance

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This patch caches all dirty pages logging until the used ring index
is updated.

The goal of this optimization is to fix a performance regression
introduced when the vhost library started to use atomic operations
to set bits in the shared dirty log map. While the fix was valid
as previous implementation wasn't safe against concurrent accesses,
contention was induced.

With this patch, during migration, we have:
1. Less atomic operations as only a single atomic OR operation
per 32 or 64 (depending on CPU) pages.
2. Less atomic operations as during a burst, the same page will
be marked dirty only once.
3. Less write memory barriers.

Fixes: 897f13a1f7 ("vhost: make page logging atomic")
Cc: stable@dpdk.org

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>
This commit is contained in:
Maxime Coquelin 2018-05-17 13:44:47 +02:00 committed by Ferruh Yigit
parent 34511c25d5
commit c16915b871
2 changed files with 137 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

119
lib/librte_vhost/vhost.h
View File

@ -36,6 +36,8 @@
#define BUF_VECTOR_MAX 256
#define VHOST_LOG_CACHE_NR 32
/**
* Structure contains buffer address, length and descriptor index
* from vring to do scatter RX.
@ -69,6 +71,14 @@ struct batch_copy_elem {
uint64_t log_addr;
};
/*
* Structure that contains the info for batched dirty logging.
*/
struct log_cache_entry {
uint32_t offset;
unsigned long val;
};
/**
* Structure contains variables relevant to RX/TX virtqueues.
*/
@ -112,6 +122,9 @@ struct vhost_virtqueue {
struct batch_copy_elem *batch_copy_elems;
uint16_t batch_copy_nb_elems;
struct log_cache_entry log_cache[VHOST_LOG_CACHE_NR];
uint16_t log_cache_nb_elem;
rte_rwlock_t iotlb_lock;
rte_rwlock_t iotlb_pending_lock;
struct rte_mempool *iotlb_pool;
@ -309,7 +322,15 @@ struct virtio_net {
static __rte_always_inline void
vhost_set_bit(unsigned int nr, volatile uint8_t *addr)
{
__sync_fetch_and_or_8(addr, (1U << nr));
#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION < 70100)
/*
* __sync_ built-ins are deprecated, but __atomic_ ones
* are sub-optimized in older GCC versions.
*/
__sync_fetch_and_or_1(addr, (1U << nr));
#else
__atomic_fetch_or(addr, (1U << nr), __ATOMIC_RELAXED);
#endif
}
static __rte_always_inline void
@ -340,6 +361,102 @@ vhost_log_write(struct virtio_net *dev, uint64_t addr, uint64_t len)
}
}
static __rte_always_inline void
vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq)
{
unsigned long *log_base;
int i;
if (likely(((dev->features & (1ULL << VHOST_F_LOG_ALL)) == 0) ||
!dev->log_base))
return;
log_base = (unsigned long *)(uintptr_t)dev->log_base;
/*
* It is expected a write memory barrier has been issued
* before this function is called.
*/
for (i = 0; i < vq->log_cache_nb_elem; i++) {
struct log_cache_entry *elem = vq->log_cache + i;
#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION < 70100)
/*
* '__sync' builtins are deprecated, but '__atomic' ones
* are sub-optimized in older GCC versions.
*/
__sync_fetch_and_or(log_base + elem->offset, elem->val);
#else
__atomic_fetch_or(log_base + elem->offset, elem->val,
__ATOMIC_RELAXED);
#endif
}
rte_smp_wmb();
vq->log_cache_nb_elem = 0;
}
static __rte_always_inline void
vhost_log_cache_page(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint64_t page)
{
uint32_t bit_nr = page % (sizeof(unsigned long) << 3);
uint32_t offset = page / (sizeof(unsigned long) << 3);
int i;
for (i = 0; i < vq->log_cache_nb_elem; i++) {
struct log_cache_entry *elem = vq->log_cache + i;
if (elem->offset == offset) {
elem->val |= (1UL << bit_nr);
return;
}
}
if (unlikely(i >= VHOST_LOG_CACHE_NR)) {
/*
* No more room for a new log cache entry,
* so write the dirty log map directly.
*/
rte_smp_wmb();
vhost_log_page((uint8_t *)(uintptr_t)dev->log_base, page);
return;
}
vq->log_cache[i].offset = offset;
vq->log_cache[i].val = (1UL << bit_nr);
}
static __rte_always_inline void
vhost_log_cache_write(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint64_t addr, uint64_t len)
{
uint64_t page;
if (likely(((dev->features & (1ULL << VHOST_F_LOG_ALL)) == 0) ||
!dev->log_base || !len))
return;
if (unlikely(dev->log_size <= ((addr + len - 1) / VHOST_LOG_PAGE / 8)))
return;
page = addr / VHOST_LOG_PAGE;
while (page * VHOST_LOG_PAGE < addr + len) {
vhost_log_cache_page(dev, vq, page);
page += 1;
}
}
static __rte_always_inline void
vhost_log_cache_used_vring(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint64_t offset, uint64_t len)
{
vhost_log_cache_write(dev, vq, vq->log_guest_addr + offset, len);
}
static __rte_always_inline void
vhost_log_used_vring(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint64_t offset, uint64_t len)

29
lib/librte_vhost/virtio_net.c
View File

@ -78,7 +78,7 @@ do_flush_shadow_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
rte_memcpy(&vq->used->ring[to],
&vq->shadow_used_ring[from],
size * sizeof(struct vring_used_elem));
vhost_log_used_vring(dev, vq,
vhost_log_cache_used_vring(dev, vq,
offsetof(struct vring_used, ring[to]),
size * sizeof(struct vring_used_elem));
}
@ -106,6 +106,8 @@ flush_shadow_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq)
rte_smp_wmb();
vhost_log_cache_sync(dev, vq);
*(volatile uint16_t *)&vq->used->idx += vq->shadow_used_idx;
vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
sizeof(vq->used->idx));
@ -130,7 +132,7 @@ do_data_copy_enqueue(struct virtio_net *dev, struct vhost_virtqueue *vq)
for (i = 0; i < count; i++) {
rte_memcpy(elem[i].dst, elem[i].src, elem[i].len);
vhost_log_write(dev, elem[i].log_addr, elem[i].len);
vhost_log_cache_write(dev, vq, elem[i].log_addr, elem[i].len);
PRINT_PACKET(dev, (uintptr_t)elem[i].dst, elem[i].len, 0);
}
}
@ -251,7 +253,7 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
virtio_enqueue_offload(m,
(struct virtio_net_hdr *)(uintptr_t)desc_addr);
PRINT_PACKET(dev, (uintptr_t)desc_addr, dev->vhost_hlen, 0);
vhost_log_write(dev, desc_gaddr, dev->vhost_hlen);
vhost_log_cache_write(dev, vq, desc_gaddr, dev->vhost_hlen);
} else {
struct virtio_net_hdr vnet_hdr;
uint64_t remain = dev->vhost_hlen;
@ -274,7 +276,7 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
(void *)(uintptr_t)src, len);
PRINT_PACKET(dev, (uintptr_t)dst, (uint32_t)len, 0);
vhost_log_write(dev, guest_addr, len);
vhost_log_cache_write(dev, vq, guest_addr, len);
remain -= len;
guest_addr += len;
src += len;
@ -355,7 +357,8 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
desc_offset)),
rte_pktmbuf_mtod_offset(m, void *, mbuf_offset),
cpy_len);
vhost_log_write(dev, desc_gaddr + desc_offset, cpy_len);
vhost_log_cache_write(dev, vq, desc_gaddr + desc_offset,
cpy_len);
PRINT_PACKET(dev, (uintptr_t)(desc_addr + desc_offset),
cpy_len, 0);
} else {
@ -444,7 +447,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
vq->used->ring[used_idx].id = desc_indexes[i];
vq->used->ring[used_idx].len = pkts[i]->pkt_len +
dev->vhost_hlen;
vhost_log_used_vring(dev, vq,
vhost_log_cache_used_vring(dev, vq,
offsetof(struct vring_used, ring[used_idx]),
sizeof(vq->used->ring[used_idx]));
}
@ -504,6 +507,8 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
rte_smp_wmb();
vhost_log_cache_sync(dev, vq);
*(volatile uint16_t *)&vq->used->idx += count;
vq->last_used_idx += count;
vhost_log_used_vring(dev, vq,
@ -767,7 +772,8 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
PRINT_PACKET(dev, (uintptr_t)dst,
(uint32_t)len, 0);
vhost_log_write(dev, guest_addr, len);
vhost_log_cache_write(dev, vq,
guest_addr, len);
remain -= len;
guest_addr += len;
@ -776,7 +782,7 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
} else {
PRINT_PACKET(dev, (uintptr_t)hdr_addr,
dev->vhost_hlen, 0);
vhost_log_write(dev, hdr_phys_addr,
vhost_log_cache_write(dev, vq, hdr_phys_addr,
dev->vhost_hlen);
}
@ -790,7 +796,8 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
desc_offset)),
rte_pktmbuf_mtod_offset(m, void *, mbuf_offset),
cpy_len);
vhost_log_write(dev, desc_gaddr + desc_offset, cpy_len);
vhost_log_cache_write(dev, vq, desc_gaddr + desc_offset,
cpy_len);
PRINT_PACKET(dev, (uintptr_t)(desc_addr + desc_offset),
cpy_len, 0);
} else {
@ -1320,7 +1327,7 @@ update_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
{
vq->used->ring[used_idx].id = desc_idx;
vq->used->ring[used_idx].len = 0;
vhost_log_used_vring(dev, vq,
vhost_log_cache_used_vring(dev, vq,
offsetof(struct vring_used, ring[used_idx]),
sizeof(vq->used->ring[used_idx]));
}
@ -1335,6 +1342,8 @@ update_used_idx(struct virtio_net *dev, struct vhost_virtqueue *vq,
rte_smp_wmb();
rte_smp_rmb();
vhost_log_cache_sync(dev, vq);
vq->used->idx += count;
vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
sizeof(vq->used->idx));