Re: [PATCH 2/3] vhost-net: Unify the code of mergeable and big buffer handling

Jason Wang
2011-01-18T07:41:25Z

Michael S. Tsirkin writes:
> On Tue, Jan 18, 2011 at 11:05:33AM +0800, Jason Wang wrote:
> > Michael S. Tsirkin writes:
> > > On Mon, Jan 17, 2011 at 04:11:08PM +0800, Jason Wang wrote:
> > > > Codes duplication were found between the handling of mergeable and big
> > > > buffers, so this patch tries to unify them. This could be easily done
> > > > by adding a quota to the get_rx_bufs() which is used to limit the
> > > > number of buffers it returns (for mergeable buffer, the quota is
> > > > simply UIO_MAXIOV, for big buffers, the quota is just 1), and then the
> > > > previous handle_rx_mergeable() could be resued also for big buffers.
> > > >
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > >
> > > We actually started this way. However the code turned out
> > > to have measureable overhead when handle_rx_mergeable
> > > is called with quota 1.
> > > So before applying this I'd like to see some data
> > > to show this is not the case anymore.
> > >
> >
> > I've run a round of test (Host->Guest) for these three patches on my desktop:
>
> Yes but what if you only apply patch 3?
>

Result here, slightly better than without it but worse than applying all the three
patches except for big buffer size at 2048 but the differnece could be neglected.

mergeable buffers:
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.66.91.161 (10.66.91.161) port 0 AF_INET
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

87380 16384 64 60.00 584.91 69.41 26.10 38.882 7.310
87380 16384 256 60.00 1194.05 72.81 34.82 19.980 4.778
87380 16384 512 60.00 1503.93 74.23 36.86 16.174 4.016
87380 16384 1024 60.00 2004.57 73.53 37.59 12.019 3.073
87380 16384 2048 60.00 3445.96 73.76 38.88 7.014 1.849

big buffers:
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.66.91.129 (10.66.91.129) port 0 AF_INET
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

87380 16384 64 60.00 646.95 72.25 27.05 36.595 6.850
87380 16384 256 60.00 1258.61 74.88 33.01 19.495 4.297
87380 16384 512 60.00 1655.95 74.14 33.96 14.671 3.360
87380 16384 1024 60.00 3220.32 74.24 33.31 7.555 1.695
87380 16384 2048 60.00 4516.40 73.88 42.10 5.360 1.527

> > Without these patches
> >
> > mergeable buffers:
> > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.66.91.42 (10.66.91.42) port 0 AF_INET
> > Recv Send Send Utilization Service Demand
> > Socket Socket Message Elapsed Send Recv Send Recv
> > Size Size Size Time Throughput local remote local remote
> > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
> >
> > 87380 16384 64 60.00 575.87 69.20 26.36 39.375 7.499
> > 87380 16384 256 60.01 1123.57 73.16 34.73 21.335 5.064
> > 87380 16384 512 60.00 1351.12 75.26 35.80 18.251 4.341
> > 87380 16384 1024 60.00 1955.31 74.73 37.67 12.523 3.156
> > 87380 16384 2048 60.01 3411.92 74.82 39.49 7.186 1.896
> >
> > bug buffers:
> > Netperf test results
> > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.66.91.109 (10.66.91.109) port 0 AF_INET
> > Recv Send Send Utilization Service Demand
> > Socket Socket Message Elapsed Send Recv Send Recv
> > Size Size Size Time Throughput local remote local remote
> > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
> >
> > 87380 16384 64 60.00 567.10 72.06 26.13 41.638 7.550
> > 87380 16384 256 60.00 1143.69 74.66 32.58 21.392 4.667
> > 87380 16384 512 60.00 1460.92 73.94 33.40 16.585 3.746
> > 87380 16384 1024 60.00 3454.85 77.49 33.89 7.349 1.607
> > 87380 16384 2048 60.00 3781.11 76.51 38.38 6.631 1.663
> >
> > With these patches:
> >
> > mergeable buffers:
> > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.66.91.236 (10.66.91.236) port 0 AF_INET
> > Recv Send Send Utilization Service Demand
> > Socket Socket Message Elapsed Send Recv Send Recv
> > Size Size Size Time Throughput local remote local remote
> > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
> >
> > 87380 16384 64 60.00 657.53 71.27 26.42 35.517 6.583
> > 87380 16384 256 60.00 1217.73 74.34 34.67 20.004 4.665
> > 87380 16384 512 60.00 1575.25 75.27 37.12 15.658 3.861
> > 87380 16384 1024 60.00 2416.07 74.77 37.20 10.140 2.522
> > 87380 16384 2048 60.00 3702.29 77.31 36.29 6.842 1.606
> >
> > big buffers:
> > Netperf test results
> > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.66.91.202 (10.66.91.202) port 0 AF_INET
> > Recv Send Send Utilization Service Demand
> > Socket Socket Message Elapsed Send Recv Send Recv
> > Size Size Size Time Throughput local remote local remote
> > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
> >
> > 87380 16384 64 60.00 647.67 71.86 27.26 36.356 6.895
> > 87380 16384 256 60.00 1265.82 76.19 36.54 19.724 4.729
> > 87380 16384 512 60.00 1796.64 76.06 39.48 13.872 3.601
> > 87380 16384 1024 60.00 4008.37 77.05 36.47 6.299 1.491
> > 87380 16384 2048 60.00 4468.56 75.18 41.79 5.513 1.532
> >
> > Looks like the unification does not hurt the performance, and with those patches
> > we can get some improvement. BTW, the regression of mergeable buffer still
> > exist.
> >
> > > > ---
> > > > drivers/vhost/net.c | 128 +++------------------------------------------------
> > > > 1 files changed, 7 insertions(+), 121 deletions(-)
> > > >
> > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > > > index 95e49de..c32a2e4 100644
> > > > --- a/drivers/vhost/net.c
> > > > +++ b/drivers/vhost/net.c
> > > > @@ -227,6 +227,7 @@ static int peek_head_len(struct sock *sk)
> > > > * @iovcount - returned count of io vectors we fill
> > > > * @log - vhost log
> > > > * @log_num - log offset
> > > > + * @quota - headcount quota, 1 for big buffer
> > > > * returns number of buffer heads allocated, negative on error
> > > > */
> > > > static int get_rx_bufs(struct vhost_virtqueue *vq,
> > > > @@ -234,7 +235,8 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
> > > > int datalen,
> > > > unsigned *iovcount,
> > > > struct vhost_log *log,
> > > > - unsigned *log_num)
> > > > + unsigned *log_num,
> > > > + unsigned int quota)
> > > > {
> > > > unsigned int out, in;
> > > > int seg = 0;
> > > > @@ -242,7 +244,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
> > > > unsigned d;
> > > > int r, nlogs = 0;
> > > >
> > > > - while (datalen > 0) {
> > > > + while (datalen > 0 && headcount < quota) {
> > > > if (unlikely(seg >= UIO_MAXIOV)) {
> > > > r = -ENOBUFS;
> > > > goto err;
> > > > @@ -282,116 +284,7 @@ err:
> > > >
> > > > /* Expects to be always run from workqueue - which acts as
> > > > * read-size critical section for our kind of RCU. */
> > > > -static void handle_rx_big(struct vhost_net *net)
> > > > -{
> > > > - struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
> > > > - unsigned out, in, log, s;
> > > > - int head;
> > > > - struct vhost_log *vq_log;
> > > > - struct msghdr msg = {
> > > > - .msg_name = NULL,
> > > > - .msg_namelen = 0,
> > > > - .msg_control = NULL, /* FIXME: get and handle RX aux data. */
> > > > - .msg_controllen = 0,
> > > > - .msg_iov = vq->iov,
> > > > - .msg_flags = MSG_DONTWAIT,
> > > > - };
> > > > -
> > > > - struct virtio_net_hdr hdr = {
> > > > - .flags = 0,
> > > > - .gso_type = VIRTIO_NET_HDR_GSO_NONE
> > > > - };
> > > > -
> > > > - size_t len, total_len = 0;
> > > > - int err;
> > > > - size_t hdr_size;
> > > > - struct socket *sock = rcu_dereference(vq->private_data);
> > > > - if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
> > > > - return;
> > > > -
> > > > - mutex_lock(&vq->mutex);
> > > > - vhost_disable_notify(vq);
> > > > - hdr_size = vq->vhost_hlen;
> > > > -
> > > > - vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
> > > > - vq->log : NULL;
> > > > -
> > > > - for (;;) {
> > > > - head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
> > > > - ARRAY_SIZE(vq->iov),
> > > > - &out, &in,
> > > > - vq_log, &log);
> > > > - /* On error, stop handling until the next kick. */
> > > > - if (unlikely(head < 0))
> > > > - break;
> > > > - /* OK, now we need to know about added descriptors. */
> > > > - if (head == vq->num) {
> > > > - if (unlikely(vhost_enable_notify(vq))) {
> > > > - /* They have slipped one in as we were
> > > > - * doing that: check again. */
> > > > - vhost_disable_notify(vq);
> > > > - continue;
> > > > - }
> > > > - /* Nothing new? Wait for eventfd to tell us
> > > > - * they refilled. */
> > > > - break;
> > > > - }
> > > > - /* We don't need to be notified again. */
> > > > - if (out) {
> > > > - vq_err(vq, "Unexpected descriptor format for RX: "
> > > > - "out %d, int %d\n",
> > > > - out, in);
> > > > - break;
> > > > - }
> > > > - /* Skip header. TODO: support TSO/mergeable rx buffers. */
> > > > - s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, in);
> > > > - msg.msg_iovlen = in;
> > > > - len = iov_length(vq->iov, in);
> > > > - /* Sanity check */
> > > > - if (!len) {
> > > > - vq_err(vq, "Unexpected header len for RX: "
> > > > - "%zd expected %zd\n",
> > > > - iov_length(vq->hdr, s), hdr_size);
> > > > - break;
> > > > - }
> > > > - err = sock->ops->recvmsg(NULL, sock, &msg,
> > > > - len, MSG_DONTWAIT | MSG_TRUNC);
> > > > - /* TODO: Check specific error and bomb out unless EAGAIN? */
> > > > - if (err < 0) {
> > > > - vhost_discard_vq_desc(vq, 1);
> > > > - break;
> > > > - }
> > > > - /* TODO: Should check and handle checksum. */
> > > > - if (err > len) {
> > > > - pr_debug("Discarded truncated rx packet: "
> > > > - " len %d > %zd\n", err, len);
> > > > - vhost_discard_vq_desc(vq, 1);
> > > > - continue;
> > > > - }
> > > > - len = err;
> > > > - err = memcpy_toiovec(vq->hdr, (unsigned char *)&hdr, hdr_size);
> > > > - if (err) {
> > > > - vq_err(vq, "Unable to write vnet_hdr at addr %p: %d\n",
> > > > - vq->iov->iov_base, err);
> > > > - break;
> > > > - }
> > > > - len += hdr_size;
> > > > - vhost_add_used_and_signal(&net->dev, vq, head, len);
> > > > - if (unlikely(vq_log))
> > > > - vhost_log_write(vq, vq_log, log, len);
> > > > - total_len += len;
> > > > - if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
> > > > - vhost_poll_queue(&vq->poll);
> > > > - break;
> > > > - }
> > > > - }
> > > > -
> > > > - mutex_unlock(&vq->mutex);
> > > > -}
> > > > -
> > > > -/* Expects to be always run from workqueue - which acts as
> > > > - * read-size critical section for our kind of RCU. */
> > > > -static void handle_rx_mergeable(struct vhost_net *net)
> > > > +static void handle_rx(struct vhost_net *net)
> > > > {
> > > > struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
> > > > unsigned uninitialized_var(in), log;
> > > > @@ -431,7 +324,8 @@ static void handle_rx_mergeable(struct vhost_net *net)
> > > > sock_len += sock_hlen;
> > > > vhost_len = sock_len + vhost_hlen;
> > > > headcount = get_rx_bufs(vq, vq->heads, vhost_len,
> > > > - &in, vq_log, &log);
> > > > + &in, vq_log, &log,
> > > > + likely(mergeable) ? UIO_MAXIOV : 1);
> > > > /* On error, stop handling until the next kick. */
> > > > if (unlikely(headcount < 0))
> > > > break;
> > > > @@ -497,14 +391,6 @@ static void handle_rx_mergeable(struct vhost_net *net)
> > > > mutex_unlock(&vq->mutex);
> > > > }
> > > >
> > > > -static void handle_rx(struct vhost_net *net)
> > > > -{
> > > > - if (vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF))
> > > > - handle_rx_mergeable(net);
> > > > - else
> > > > - handle_rx_big(net);
> > > > -}
> > > > -
> > > > static void handle_tx_kick(struct vhost_work *work)
> > > > {
> > > > struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,