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Date: Wed, 27 Sep 2023 09:50:06 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: virtualization@...ts.linux-foundation.org,
Jason Wang <jasowang@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
netdev@...r.kernel.org,
bpf@...r.kernel.org,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH vhost v13 12/12] virtio_net: merge dma operations when filling mergeable buffers
On Tue, 26 Sep 2023 12:01:34 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Thu, Aug 10, 2023 at 08:30:57PM +0800, Xuan Zhuo wrote:
> > Currently, the virtio core will perform a dma operation for each
> > buffer. Although, the same page may be operated multiple times.
> >
> > This patch, the driver does the dma operation and manages the dma
> > address based the feature premapped of virtio core.
> >
> > This way, we can perform only one dma operation for the pages of the
> > alloc frag. This is beneficial for the iommu device.
> >
> > kernel command line: intel_iommu=on iommu.passthrough=0
> >
> > | strict=0 | strict=1
> > Before | 775496pps | 428614pps
> > After | 1109316pps | 742853pps
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>
> Hi Xuan Zhuo,
> looks like this patch is causing regressions. Do you have time to debug
> or should I revert?
I have sended a fix to Michael Roth.
I will wait his response. If that is ok, I will post that fix commit.
Thanks.
>
> > ---
> > drivers/net/virtio_net.c | 228 ++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 202 insertions(+), 26 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 486b5849033d..16adb5ef18f8 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -126,6 +126,14 @@ static const struct virtnet_stat_desc virtnet_rq_stats_desc[] = {
> > #define VIRTNET_SQ_STATS_LEN ARRAY_SIZE(virtnet_sq_stats_desc)
> > #define VIRTNET_RQ_STATS_LEN ARRAY_SIZE(virtnet_rq_stats_desc)
> >
> > +/* The dma information of pages allocated at a time. */
> > +struct virtnet_rq_dma {
> > + dma_addr_t addr;
> > + u32 ref;
> > + u16 len;
> > + u16 need_sync;
> > +};
> > +
> > /* Internal representation of a send virtqueue */
> > struct send_queue {
> > /* Virtqueue associated with this send _queue */
> > @@ -175,6 +183,12 @@ struct receive_queue {
> > char name[16];
> >
> > struct xdp_rxq_info xdp_rxq;
> > +
> > + /* Record the last dma info to free after new pages is allocated. */
> > + struct virtnet_rq_dma *last_dma;
> > +
> > + /* Do dma by self */
> > + bool do_dma;
> > };
> >
> > /* This structure can contain rss message with maximum settings for indirection table and keysize
> > @@ -549,6 +563,156 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> > return skb;
> > }
> >
> > +static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
> > +{
> > + struct page *page = virt_to_head_page(buf);
> > + struct virtnet_rq_dma *dma;
> > + void *head;
> > + int offset;
> > +
> > + head = page_address(page);
> > +
> > + dma = head;
> > +
> > + --dma->ref;
> > +
> > + if (dma->ref) {
> > + if (dma->need_sync && len) {
> > + offset = buf - (head + sizeof(*dma));
> > +
> > + virtqueue_dma_sync_single_range_for_cpu(rq->vq, dma->addr, offset,
> > + len, DMA_FROM_DEVICE);
> > + }
> > +
> > + return;
> > + }
> > +
> > + virtqueue_dma_unmap_single_attrs(rq->vq, dma->addr, dma->len,
> > + DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
> > + put_page(page);
> > +}
> > +
> > +static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
> > +{
> > + void *buf;
> > +
> > + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > + if (buf && rq->do_dma)
> > + virtnet_rq_unmap(rq, buf, *len);
> > +
> > + return buf;
> > +}
> > +
> > +static void *virtnet_rq_detach_unused_buf(struct receive_queue *rq)
> > +{
> > + void *buf;
> > +
> > + buf = virtqueue_detach_unused_buf(rq->vq);
> > + if (buf && rq->do_dma)
> > + virtnet_rq_unmap(rq, buf, 0);
> > +
> > + return buf;
> > +}
> > +
> > +static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> > +{
> > + struct virtnet_rq_dma *dma;
> > + dma_addr_t addr;
> > + u32 offset;
> > + void *head;
> > +
> > + if (!rq->do_dma) {
> > + sg_init_one(rq->sg, buf, len);
> > + return;
> > + }
> > +
> > + head = page_address(rq->alloc_frag.page);
> > +
> > + offset = buf - head;
> > +
> > + dma = head;
> > +
> > + addr = dma->addr - sizeof(*dma) + offset;
> > +
> > + sg_init_table(rq->sg, 1);
> > + rq->sg[0].dma_address = addr;
> > + rq->sg[0].length = len;
> > +}
> > +
> > +static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> > +{
> > + struct page_frag *alloc_frag = &rq->alloc_frag;
> > + struct virtnet_rq_dma *dma;
> > + void *buf, *head;
> > + dma_addr_t addr;
> > +
> > + if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
> > + return NULL;
> > +
> > + head = page_address(alloc_frag->page);
> > +
> > + if (rq->do_dma) {
> > + dma = head;
> > +
> > + /* new pages */
> > + if (!alloc_frag->offset) {
> > + if (rq->last_dma) {
> > + /* Now, the new page is allocated, the last dma
> > + * will not be used. So the dma can be unmapped
> > + * if the ref is 0.
> > + */
> > + virtnet_rq_unmap(rq, rq->last_dma, 0);
> > + rq->last_dma = NULL;
> > + }
> > +
> > + dma->len = alloc_frag->size - sizeof(*dma);
> > +
> > + addr = virtqueue_dma_map_single_attrs(rq->vq, dma + 1,
> > + dma->len, DMA_FROM_DEVICE, 0);
> > + if (virtqueue_dma_mapping_error(rq->vq, addr))
> > + return NULL;
> > +
> > + dma->addr = addr;
> > + dma->need_sync = virtqueue_dma_need_sync(rq->vq, addr);
> > +
> > + /* Add a reference to dma to prevent the entire dma from
> > + * being released during error handling. This reference
> > + * will be freed after the pages are no longer used.
> > + */
> > + get_page(alloc_frag->page);
> > + dma->ref = 1;
> > + alloc_frag->offset = sizeof(*dma);
> > +
> > + rq->last_dma = dma;
> > + }
> > +
> > + ++dma->ref;
> > + }
> > +
> > + buf = head + alloc_frag->offset;
> > +
> > + get_page(alloc_frag->page);
> > + alloc_frag->offset += size;
> > +
> > + return buf;
> > +}
> > +
> > +static void virtnet_rq_set_premapped(struct virtnet_info *vi)
> > +{
> > + int i;
> > +
> > + /* disable for big mode */
> > + if (!vi->mergeable_rx_bufs && vi->big_packets)
> > + return;
> > +
> > + for (i = 0; i < vi->max_queue_pairs; i++) {
> > + if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> > + continue;
> > +
> > + vi->rq[i].do_dma = true;
> > + }
> > +}
> > +
> > static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
> > {
> > unsigned int len;
> > @@ -835,7 +999,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> > void *buf;
> > int off;
> >
> > - buf = virtqueue_get_buf(rq->vq, &buflen);
> > + buf = virtnet_rq_get_buf(rq, &buflen, NULL);
> > if (unlikely(!buf))
> > goto err_buf;
> >
> > @@ -1126,7 +1290,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> > return -EINVAL;
> >
> > while (--*num_buf > 0) {
> > - buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> > + buf = virtnet_rq_get_buf(rq, &len, &ctx);
> > if (unlikely(!buf)) {
> > pr_debug("%s: rx error: %d buffers out of %d missing\n",
> > dev->name, *num_buf,
> > @@ -1351,7 +1515,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > while (--num_buf) {
> > int num_skb_frags;
> >
> > - buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> > + buf = virtnet_rq_get_buf(rq, &len, &ctx);
> > if (unlikely(!buf)) {
> > pr_debug("%s: rx error: %d buffers out of %d missing\n",
> > dev->name, num_buf,
> > @@ -1414,7 +1578,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > err_skb:
> > put_page(page);
> > while (num_buf-- > 1) {
> > - buf = virtqueue_get_buf(rq->vq, &len);
> > + buf = virtnet_rq_get_buf(rq, &len, NULL);
> > if (unlikely(!buf)) {
> > pr_debug("%s: rx error: %d buffers missing\n",
> > dev->name, num_buf);
> > @@ -1524,7 +1688,6 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> > static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> > gfp_t gfp)
> > {
> > - struct page_frag *alloc_frag = &rq->alloc_frag;
> > char *buf;
> > unsigned int xdp_headroom = virtnet_get_headroom(vi);
> > void *ctx = (void *)(unsigned long)xdp_headroom;
> > @@ -1533,17 +1696,21 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> >
> > len = SKB_DATA_ALIGN(len) +
> > SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > - if (unlikely(!skb_page_frag_refill(len, alloc_frag, gfp)))
> > +
> > + buf = virtnet_rq_alloc(rq, len, gfp);
> > + if (unlikely(!buf))
> > return -ENOMEM;
> >
> > - buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> > - get_page(alloc_frag->page);
> > - alloc_frag->offset += len;
> > - sg_init_one(rq->sg, buf + VIRTNET_RX_PAD + xdp_headroom,
> > - vi->hdr_len + GOOD_PACKET_LEN);
> > + virtnet_rq_init_one_sg(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
> > + vi->hdr_len + GOOD_PACKET_LEN);
> > +
> > err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > - if (err < 0)
> > + if (err < 0) {
> > + if (rq->do_dma)
> > + virtnet_rq_unmap(rq, buf, 0);
> > put_page(virt_to_head_page(buf));
> > + }
> > +
> > return err;
> > }
> >
> > @@ -1620,23 +1787,22 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > unsigned int headroom = virtnet_get_headroom(vi);
> > unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> > unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> > - char *buf;
> > + unsigned int len, hole;
> > void *ctx;
> > + char *buf;
> > int err;
> > - unsigned int len, hole;
> >
> > /* Extra tailroom is needed to satisfy XDP's assumption. This
> > * means rx frags coalescing won't work, but consider we've
> > * disabled GSO for XDP, it won't be a big issue.
> > */
> > len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> > - if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> > +
> > + buf = virtnet_rq_alloc(rq, len + room, gfp);
> > + if (unlikely(!buf))
> > return -ENOMEM;
> >
> > - buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> > buf += headroom; /* advance address leaving hole at front of pkt */
> > - get_page(alloc_frag->page);
> > - alloc_frag->offset += len + room;
> > hole = alloc_frag->size - alloc_frag->offset;
> > if (hole < len + room) {
> > /* To avoid internal fragmentation, if there is very likely not
> > @@ -1650,11 +1816,15 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > alloc_frag->offset += hole;
> > }
> >
> > - sg_init_one(rq->sg, buf, len);
> > + virtnet_rq_init_one_sg(rq, buf, len);
> > +
> > ctx = mergeable_len_to_ctx(len + room, headroom);
> > err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > - if (err < 0)
> > + if (err < 0) {
> > + if (rq->do_dma)
> > + virtnet_rq_unmap(rq, buf, 0);
> > put_page(virt_to_head_page(buf));
> > + }
> >
> > return err;
> > }
> > @@ -1775,13 +1945,13 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
> > void *ctx;
> >
> > while (stats.packets < budget &&
> > - (buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx))) {
> > + (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> > receive_buf(vi, rq, buf, len, ctx, xdp_xmit, &stats);
> > stats.packets++;
> > }
> > } else {
> > while (stats.packets < budget &&
> > - (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> > + (buf = virtnet_rq_get_buf(rq, &len, NULL)) != NULL) {
> > receive_buf(vi, rq, buf, len, NULL, xdp_xmit, &stats);
> > stats.packets++;
> > }
> > @@ -3553,8 +3723,11 @@ static void free_receive_page_frags(struct virtnet_info *vi)
> > {
> > int i;
> > for (i = 0; i < vi->max_queue_pairs; i++)
> > - if (vi->rq[i].alloc_frag.page)
> > + if (vi->rq[i].alloc_frag.page) {
> > + if (vi->rq[i].do_dma && vi->rq[i].last_dma)
> > + virtnet_rq_unmap(&vi->rq[i], vi->rq[i].last_dma, 0);
> > put_page(vi->rq[i].alloc_frag.page);
> > + }
> > }
> >
> > static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> > @@ -3591,9 +3764,10 @@ static void free_unused_bufs(struct virtnet_info *vi)
> > }
> >
> > for (i = 0; i < vi->max_queue_pairs; i++) {
> > - struct virtqueue *vq = vi->rq[i].vq;
> > - while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> > - virtnet_rq_free_unused_buf(vq, buf);
> > + struct receive_queue *rq = &vi->rq[i];
> > +
> > + while ((buf = virtnet_rq_detach_unused_buf(rq)) != NULL)
> > + virtnet_rq_free_unused_buf(rq->vq, buf);
> > cond_resched();
> > }
> > }
> > @@ -3767,6 +3941,8 @@ static int init_vqs(struct virtnet_info *vi)
> > if (ret)
> > goto err_free;
> >
> > + virtnet_rq_set_premapped(vi);
> > +
> > cpus_read_lock();
> > virtnet_set_affinity(vi);
> > cpus_read_unlock();
> > --
> > 2.32.0.3.g01195cf9f
>
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