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[PATCH net-next V2 0/5] Refine virtio-net XDP

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  [PATCH net-next V2 0/5] Refine virtio-net XDP Jason Wang <jasowang@redhat.com> - 2017-07-19 11:00 +0200
    [PATCH net-next V2 2/5] virtio-net: pack headroom into ctx for mergeable buffers Jason Wang <jasowang@redhat.com> - 2017-07-19 11:00 +0200
    Re: [PATCH net-next V2 0/5] Refine virtio-net XDP David Miller <davem@davemloft.net> - 2017-07-24 22:40 +0200
      Re: [PATCH net-next V2 0/5] Refine virtio-net XDP "Michael S. Tsirkin" <mst@redhat.com> - 2017-07-24 23:50 +0200

#1691136 — [PATCH net-next V2 0/5] Refine virtio-net XDP

Hi:

This series brings two optimizations for virtio-net XDP:

- avoid reset during XDP set
- turn off offloads on demand

Changes from V1:
- Various tweaks on commit logs and comments
- Use virtnet_napi_enable() when enabling NAPI on XDP set
- Copy the small buffer packet only if xdp_headroom is smaller than
  required

Please review.

Thanks

Jason Wang (5):
  virtio_ring: allow to store zero as the ctx
  virtio-net: pack headroom into ctx for mergeable buffers
  virtio-net: switch to use new ctx API for small buffer
  virtio-net: do not reset during XDP set
  virtio-net: switch off offloads on demand if possible on XDP set

 drivers/net/virtio_net.c     | 332 ++++++++++++++++++++++++++-----------------
 drivers/virtio/virtio_ring.c |   2 +-
 2 files changed, 200 insertions(+), 134 deletions(-)

-- 
2.7.4

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#1691139 — [PATCH net-next V2 2/5] virtio-net: pack headroom into ctx for mergeable buffers

Pack headroom into ctx - this way when we get a buffer we can figure out
the actual headroom that was allocated for the buffer. Will be helpful
to optimize switching between XDP and non-XDP modes which have different
headroom requirements.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 1f8c15c..8fae9a8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -270,6 +270,23 @@ static void skb_xmit_done(struct virtqueue *vq)
 		netif_wake_subqueue(vi->dev, vq2txq(vq));
 }
 
+#define MRG_CTX_HEADER_SHIFT 22
+static void *mergeable_len_to_ctx(unsigned int truesize,
+				  unsigned int headroom)
+{
+	return (void *)(unsigned long)((headroom << MRG_CTX_HEADER_SHIFT) | truesize);
+}
+
+static unsigned int mergeable_ctx_to_headroom(void *mrg_ctx)
+{
+	return (unsigned long)mrg_ctx >> MRG_CTX_HEADER_SHIFT;
+}
+
+static unsigned int mergeable_ctx_to_truesize(void *mrg_ctx)
+{
+	return (unsigned long)mrg_ctx & ((1 << MRG_CTX_HEADER_SHIFT) - 1);
+}
+
 /* Called from bottom half context */
 static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 				   struct receive_queue *rq,
@@ -639,13 +656,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 	}
 	rcu_read_unlock();
 
-	if (unlikely(len > (unsigned long)ctx)) {
+	truesize = mergeable_ctx_to_truesize(ctx);
+	if (unlikely(len > truesize)) {
 		pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
 			 dev->name, len, (unsigned long)ctx);
 		dev->stats.rx_length_errors++;
 		goto err_skb;
 	}
-	truesize = (unsigned long)ctx;
+
 	head_skb = page_to_skb(vi, rq, page, offset, len, truesize);
 	curr_skb = head_skb;
 
@@ -665,13 +683,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		}
 
 		page = virt_to_head_page(buf);
-		if (unlikely(len > (unsigned long)ctx)) {
+
+		truesize = mergeable_ctx_to_truesize(ctx);
+		if (unlikely(len > truesize)) {
 			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
 				 dev->name, len, (unsigned long)ctx);
 			dev->stats.rx_length_errors++;
 			goto err_skb;
 		}
-		truesize = (unsigned long)ctx;
 
 		num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
 		if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
@@ -889,7 +908,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 
 	buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
 	buf += headroom; /* advance address leaving hole at front of pkt */
-	ctx = (void *)(unsigned long)len;
+	ctx = mergeable_len_to_ctx(len, headroom);
 	get_page(alloc_frag->page);
 	alloc_frag->offset += len + headroom;
 	hole = alloc_frag->size - alloc_frag->offset;
-- 
2.7.4

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#1695075

From: Jason Wang <jasowang@redhat.com>
Date: Wed, 19 Jul 2017 16:54:44 +0800

> Hi:
> 
> This series brings two optimizations for virtio-net XDP:
> 
> - avoid reset during XDP set
> - turn off offloads on demand
> 
> Changes from V1:
> - Various tweaks on commit logs and comments
> - Use virtnet_napi_enable() when enabling NAPI on XDP set
> - Copy the small buffer packet only if xdp_headroom is smaller than
>   required
> 
> Please review.

Series applied, thanks Jason.

Michael, I gave you 4+ days to properly review this respin of this
series.  I felt that was more than sufficient time, even with an
intervening weekend.  So if you don't like that I applied this without
your review, please be more punctual in the future.

Thank you.

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#1695148

On Mon, Jul 24, 2017 at 01:38:59PM -0700, David Miller wrote:
> From: Jason Wang <jasowang@redhat.com>
> Date: Wed, 19 Jul 2017 16:54:44 +0800
> 
> > Hi:
> > 
> > This series brings two optimizations for virtio-net XDP:
> > 
> > - avoid reset during XDP set
> > - turn off offloads on demand
> > 
> > Changes from V1:
> > - Various tweaks on commit logs and comments
> > - Use virtnet_napi_enable() when enabling NAPI on XDP set
> > - Copy the small buffer packet only if xdp_headroom is smaller than
> >   required
> > 
> > Please review.
> 
> Series applied, thanks Jason.
> 
> Michael, I gave you 4+ days to properly review this respin of this
> series.  I felt that was more than sufficient time, even with an
> intervening weekend.  So if you don't like that I applied this without
> your review, please be more punctual in the future.
> 
> Thank you.

My bad - reviewed when I was offline and forgot to send it out.

By luck this is not a big deal:

- Patches 1-4 are good.
- Patch 5 has some problems IMO, but all it does
is try to enable a previously non-working configuration, so
it seems ok to fix it up with follow-up patches as appropriate.

-- 
MST

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