Re: [dpdk-dev] [PATCH] vhost: cache guest/vhost physical address mapping

[Ye Xiaolong <xiaolong.ye@intel.com>]

Hi, Marvin

On 03/16, Marvin Liu wrote:
>If Tx zero copy enabled, gpa to hpa mapping table is updated one by
>one. This will harm performance when guest memory backend using 2M
>hugepages. Now add cached mapping table which will sorted by using
>sequence. Address translation will first check cached mapping table,
>now performance is back.
>
>Signed-off-by: Marvin Liu <yong.liu@intel.com>
>
>diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
>index 2087d1400..de2c09e7e 100644
>--- a/lib/librte_vhost/vhost.h
>+++ b/lib/librte_vhost/vhost.h
>@@ -368,7 +368,9 @@ struct virtio_net {
> 	struct vhost_device_ops const *notify_ops;
> 
> 	uint32_t		nr_guest_pages;
>+	uint32_t		nr_cached;

What about naming it nr_cached_guest_pages to make it more self-explanatory
as nr_cached is too generic?

> 	uint32_t		max_guest_pages;
>+	struct guest_page       *cached_guest_pages;
> 	struct guest_page       *guest_pages;
> 
> 	int			slave_req_fd;
>@@ -554,11 +556,23 @@ gpa_to_hpa(struct virtio_net *dev, uint64_t gpa, uint64_t size)
> 	uint32_t i;
> 	struct guest_page *page;
> 
>+	for (i = 0; i < dev->nr_cached; i++) {
>+		page = &dev->cached_guest_pages[i];
>+		if (gpa >= page->guest_phys_addr &&
>+			gpa + size < page->guest_phys_addr + page->size) {
>+			return gpa - page->guest_phys_addr +
>+				page->host_phys_addr;
>+		}
>+	}
>+
> 	for (i = 0; i < dev->nr_guest_pages; i++) {
> 		page = &dev->guest_pages[i];
> 
> 		if (gpa >= page->guest_phys_addr &&
> 		    gpa + size < page->guest_phys_addr + page->size) {
>+			rte_memcpy(&dev->cached_guest_pages[dev->nr_cached],
>+				   page, sizeof(struct guest_page));
>+			dev->nr_cached++;
> 			return gpa - page->guest_phys_addr +
> 			       page->host_phys_addr;
> 		}
>diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>index bd1be0104..573e99066 100644
>--- a/lib/librte_vhost/vhost_user.c
>+++ b/lib/librte_vhost/vhost_user.c
>@@ -192,7 +192,9 @@ vhost_backend_cleanup(struct virtio_net *dev)
> 	}
> 
> 	free(dev->guest_pages);
>+	free(dev->cached_guest_pages);
> 	dev->guest_pages = NULL;
>+	dev->cached_guest_pages = NULL;
> 
> 	if (dev->log_addr) {
> 		munmap((void *)(uintptr_t)dev->log_addr, dev->log_size);
>@@ -905,7 +907,10 @@ add_one_guest_page(struct virtio_net *dev, uint64_t guest_phys_addr,
> 		old_pages = dev->guest_pages;
> 		dev->guest_pages = realloc(dev->guest_pages,
> 					dev->max_guest_pages * sizeof(*page));
>-		if (!dev->guest_pages) {
>+		dev->cached_guest_pages = realloc(dev->cached_guest_pages,
>+					dev->max_guest_pages * sizeof(*page));
>+		dev->nr_cached = 0;
>+		if (!dev->guest_pages || !dev->cached_guest_pages) {

Better to compare pointer to NULL according to DPDK's coding style.

> 			VHOST_LOG_CONFIG(ERR, "cannot realloc guest_pages\n");
> 			free(old_pages);
> 			return -1;
>@@ -1075,6 +1080,18 @@ vhost_user_set_mem_table(struct virtio_net **pdev, struct VhostUserMsg *msg,
> 		}
> 	}
> 

Do we need initialize dev->nr_cached to 0 explicitly here?

>+	if (!dev->cached_guest_pages) {
>+		dev->cached_guest_pages = malloc(dev->max_guest_pages *
>+						sizeof(struct guest_page));

I'm wondering why use malloc/realloc/free for cached_guest_pages instead of DPDK
memory allocator APIs, I can see current code uses malloc/realloc/free for guest_pages,
Is there any history reason I don't know?

Thanks,
Xiaolong

>+		if (dev->cached_guest_pages == NULL) {
>+			VHOST_LOG_CONFIG(ERR,
>+				"(%d) failed to allocate memory "
>+				"for dev->cached_guest_pages\n",
>+				dev->vid);
>+			return RTE_VHOST_MSG_RESULT_ERR;
>+		}
>+	}
>+
> 	dev->mem = rte_zmalloc("vhost-mem-table", sizeof(struct rte_vhost_memory) +
> 		sizeof(struct rte_vhost_mem_region) * memory->nregions, 0);
> 	if (dev->mem == NULL) {
>-- 
>2.17.1
>