Wanted to try this awhile now, good to see this worked on! Some comments inline.
On Wed, Aug 12, 2009 at 11:33:51PM -0700, Shirley Ma wrote: > Guest virtio_net receives packets from its pre-allocated vring > buffers, then it delivers these packets to upper layer protocols > as skb buffs. So it's not necessary to pre-allocate skb for each > mergable buffer, then frees it when it's useless. > > This patch has deferred skb allocation to when receiving packets, > it reduces skb pre-allocations and skb_frees. And it induces two > page list: freed_pages and used_page list, used_pages is used to > track pages pre-allocated, it is only useful when removing virtio_net. > > This patch has tested and measured against 2.6.31-rc4 git, > I thought this patch will improve large packet performance, but I saw > netperf TCP_STREAM performance improved for small packet for both > local guest to host and host to local guest cases. It also reduces > UDP packets drop rate from host to local guest. I am not fully understand > why. > > The netperf results from my laptop are: > > mtu=1500 > netperf -H xxx -l 120 > > w/o patch w/i patch (two runs) > guest to host: 3336.84Mb/s 3730.14Mb/s ~ 3582.88Mb/s > > host to guest: 3165.10Mb/s 3370.39Mb/s ~ 3407.96Mb/s > > Here is the patch for your review. The same approach can apply to non-mergable > buffs too, so we can use code in common. Yes, we should do that. The way to test is to hack virtio to ignore host support for mergeable buffers. > If there is no objection, I will > submit the non-mergable buffs patch later. > The whole page cache management in virtio net is too complex. Since it seems you bypass it for some cases, this might be where savings come from? > Signed-off-by: Shirley Ma <[email protected]> > --- > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 2a6e81d..e31ebc9 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -17,6 +17,7 @@ > * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA > */ > //#define DEBUG > +#include <linux/list.h> > #include <linux/netdevice.h> > #include <linux/etherdevice.h> > #include <linux/ethtool.h> > @@ -39,6 +40,12 @@ module_param(gso, bool, 0444); > > #define VIRTNET_SEND_COMMAND_SG_MAX 2 > > +struct page_list > +{ Kernel style is "struct page_list {". Also, prefix with virtnet_? > + struct page *page; > + struct list_head list; > +}; > + > struct virtnet_info > { > struct virtio_device *vdev; > @@ -72,6 +79,8 @@ struct virtnet_info > > /* Chain pages by the private ptr. */ > struct page *pages; Do we need the pages list now? Can we do without? Pls document fields below. > + struct list_head used_pages; Seems a waste to have this list just for dev down. Extend virtio to give us all buffers from vq on shutdown? > + struct list_head freed_pages; > }; > > static inline void *skb_vnet_hdr(struct sk_buff *skb) > @@ -106,6 +115,26 @@ static struct page *get_a_page(struct virtnet_info *vi, > gfp_t gfp_mask) > return p; > } > > +static struct page_list *get_a_free_page(struct virtnet_info *vi, gfp_t > gfp_mask) always called with gfp_mask GFP_ATOMIC? Also - line too long here and elsewere. Run checkpatch? > +{ > + struct page_list *plist; > + > + if (list_empty(&vi->freed_pages)) { special handling for empty list looks a bit ugly really necessary? > + plist = kmalloc(sizeof(struct page_list), gfp_mask); sizeof *plist > + if (!plist) > + return NULL; > + list_add_tail(&plist->list, &vi->freed_pages); > + plist->page = alloc_page(gfp_mask); > + } else { > + plist = list_first_entry(&vi->freed_pages, struct page_list, > list); is the first entry special? pls document in struct definition > + if (!plist->page) > + plist->page = alloc_page(gfp_mask); what does it mean plist->page == NULL? Please document this in struct definition. > + } > + if (plist->page) > + list_move_tail(&plist->list, &vi->used_pages); > + return plist; > +} > + > static void skb_xmit_done(struct virtqueue *svq) > { > struct virtnet_info *vi = svq->vdev->priv; > @@ -121,14 +150,14 @@ static void skb_xmit_done(struct virtqueue *svq) > tasklet_schedule(&vi->tasklet); > } > > -static void receive_skb(struct net_device *dev, struct sk_buff *skb, > +static void receive_skb(struct net_device *dev, void *buf, what is buf, here? can it have proper type and not void*? > unsigned len) > { > struct virtnet_info *vi = netdev_priv(dev); > - struct virtio_net_hdr *hdr = skb_vnet_hdr(skb); > int err; > int i; > - > + struct sk_buff *skb = NULL; > + struct virtio_net_hdr *hdr = NULL; do we have to init these to NULL? > if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) { > pr_debug("%s: short packet %i\n", dev->name, len); > dev->stats.rx_length_errors++; > @@ -136,15 +165,30 @@ static void receive_skb(struct net_device *dev, struct > sk_buff *skb, > } > > if (vi->mergeable_rx_bufs) { > - struct virtio_net_hdr_mrg_rxbuf *mhdr = skb_vnet_hdr(skb); > + struct virtio_net_hdr_mrg_rxbuf *mhdr; > unsigned int copy; > - char *p = page_address(skb_shinfo(skb)->frags[0].page); > + skb_frag_t *f; > + struct page_list *plist = (struct page_list *)buf; cast not necessary > + char *p = page_address(plist->page); > + > + skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN); > + if (unlikely(!skb)) { > + /* drop the packet */ obvious, but okay ... > + dev->stats.rx_dropped++; but what does the below do? Maybe add a comment ... > + list_move_tail(&plist->list, &vi->freed_pages); > + return; > + } > + > + skb_reserve(skb, NET_IP_ALIGN); > > if (len > PAGE_SIZE) > len = PAGE_SIZE; > len -= sizeof(struct virtio_net_hdr_mrg_rxbuf); > > - memcpy(hdr, p, sizeof(*mhdr)); > + mhdr = skb_vnet_hdr(skb); > + memcpy(mhdr, p, sizeof(*mhdr)); > + hdr = (struct virtio_net_hdr *)mhdr; > + > p += sizeof(*mhdr); > > copy = len; > @@ -155,20 +199,20 @@ static void receive_skb(struct net_device *dev, struct > sk_buff *skb, > > len -= copy; > > - if (!len) { > - give_a_page(vi, skb_shinfo(skb)->frags[0].page); > - skb_shinfo(skb)->nr_frags--; > - } else { > - skb_shinfo(skb)->frags[0].page_offset += > + if (len) { > + f = &skb_shinfo(skb)->frags[0]; > + f->page = plist->page; > + skb_shinfo(skb)->frags[0].page_offset = > sizeof(*mhdr) + copy; > skb_shinfo(skb)->frags[0].size = len; > skb->data_len += len; > skb->len += len; > + skb_shinfo(skb)->nr_frags++; > + plist->page = NULL; > } > + list_move_tail(&plist->list, &vi->freed_pages); > > while (--mhdr->num_buffers) { > - struct sk_buff *nskb; > - > i = skb_shinfo(skb)->nr_frags; > if (i >= MAX_SKB_FRAGS) { > pr_debug("%s: packet too long %d\n", dev->name, > @@ -177,30 +221,30 @@ static void receive_skb(struct net_device *dev, struct > sk_buff *skb, > goto drop; > } > > - nskb = vi->rvq->vq_ops->get_buf(vi->rvq, &len); > - if (!nskb) { > + plist = vi->rvq->vq_ops->get_buf(vi->rvq, &len); > + if (!plist) { > pr_debug("%s: rx error: %d buffers missing\n", > dev->name, mhdr->num_buffers); > dev->stats.rx_length_errors++; > goto drop; > } > - > - __skb_unlink(nskb, &vi->recv); > vi->num--; > - > - skb_shinfo(skb)->frags[i] = skb_shinfo(nskb)->frags[0]; > - skb_shinfo(nskb)->nr_frags = 0; > - kfree_skb(nskb); > - > + f = &skb_shinfo(skb)->frags[i]; > + f->page = plist->page; > + f->page_offset = 0; I though skb is pre-zeroed anyway. No? > + > if (len > PAGE_SIZE) > len = PAGE_SIZE; > - please don't change empty lines arbitrarily > skb_shinfo(skb)->frags[i].size = len; > skb_shinfo(skb)->nr_frags++; > skb->data_len += len; > skb->len += len; > + plist->page = NULL; > + list_move_tail(&plist->list, &vi->freed_pages); did we set all fields here? how about truesize? Does skb_add_rx_frag do what we want by any chance? > } > } else { > + skb = (struct sk_buff *)buf; don't cast away void > + hdr = skb_vnet_hdr(skb); > len -= sizeof(struct virtio_net_hdr); > > if (len <= MAX_PACKET_LEN) > @@ -329,7 +373,6 @@ static void try_fill_recv_maxbufs(struct virtnet_info *vi) > > static void try_fill_recv(struct virtnet_info *vi) > { > - struct sk_buff *skb; > struct scatterlist sg[1]; > int err; > > @@ -339,39 +382,21 @@ static void try_fill_recv(struct virtnet_info *vi) > } > > for (;;) { > - skb_frag_t *f; > - > - skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN); > - if (unlikely(!skb)) > - break; > - > - skb_reserve(skb, NET_IP_ALIGN); > - > - f = &skb_shinfo(skb)->frags[0]; > - f->page = get_a_page(vi, GFP_ATOMIC); > - if (!f->page) { > - kfree_skb(skb); > + struct page_list *plist = get_a_free_page(vi, GFP_ATOMIC); > + if (!plist || !plist->page) > break; > - } > - > - f->page_offset = 0; > - f->size = PAGE_SIZE; > - > - skb_shinfo(skb)->nr_frags++; > - > - sg_init_one(sg, page_address(f->page), PAGE_SIZE); > - skb_queue_head(&vi->recv, skb); > - > - err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb); > + sg_init_one(sg, page_address(plist->page), PAGE_SIZE); > + err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, plist); > if (err) { > - skb_unlink(skb, &vi->recv); > - kfree_skb(skb); > + list_move_tail(&plist->list, &vi->freed_pages); > break; > } > vi->num++; > } > + > if (unlikely(vi->num > vi->max)) > vi->max = vi->num; > + unnecessary empty lines - if you like them, make a separate patch. and seems to have trailing whitespace. > vi->rvq->vq_ops->kick(vi->rvq); > } > > @@ -388,14 +413,15 @@ static void skb_recv_done(struct virtqueue *rvq) > static int virtnet_poll(struct napi_struct *napi, int budget) > { > struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi); > - struct sk_buff *skb = NULL; > + void *buf = NULL; Does it need to be initialized? > unsigned int len, received = 0; > > again: > while (received < budget && > - (skb = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) { > - __skb_unlink(skb, &vi->recv); > - receive_skb(vi->dev, skb, len); > + (buf = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) { > + if (!vi->mergeable_rx_bufs) > + __skb_unlink((struct sk_buff *)buf, &vi->recv); cast not necessary > + receive_skb(vi->dev, buf, len); > vi->num--; > received++; > } > @@ -893,6 +919,8 @@ static int virtnet_probe(struct virtio_device *vdev) > vi->vdev = vdev; > vdev->priv = vi; > vi->pages = NULL; > + INIT_LIST_HEAD(&vi->used_pages); > + INIT_LIST_HEAD(&vi->freed_pages); > > /* If they give us a callback when all buffers are done, we don't need > * the timer. */ > @@ -969,6 +997,7 @@ static void virtnet_remove(struct virtio_device *vdev) > { > struct virtnet_info *vi = vdev->priv; > struct sk_buff *skb; > + struct page_list *plist, *tp; > > /* Stop all the virtqueues. */ > vdev->config->reset(vdev); > @@ -977,14 +1006,23 @@ static void virtnet_remove(struct virtio_device *vdev) > del_timer_sync(&vi->xmit_free_timer); > > /* Free our skbs in send and recv queues, if any. */ > - while ((skb = __skb_dequeue(&vi->recv)) != NULL) { > - kfree_skb(skb); > - vi->num--; > + if (!vi->mergeable_rx_bufs) { > + while ((skb = __skb_dequeue(&vi->recv)) != NULL) { > + kfree_skb(skb); > + vi->num--; > + } > + BUG_ON(vi->num != 0); > + } else { > + list_splice_init(&vi->used_pages, &vi->freed_pages); > + list_for_each_entry_safe(plist, tp, &vi->freed_pages, list) { > + vi->num--; > + if (plist->page) > + __free_pages(plist->page, 0); > + kfree(plist); > + } BUG_ON here as well? > } So, you are fixing this to share code. Good. > __skb_queue_purge(&vi->send); > > - BUG_ON(vi->num != 0); > - > unregister_netdev(vi->dev); > > vdev->config->del_vqs(vi->vdev); > > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
