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Date: Mon, 9 Apr 2018 05:42:30 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: haibinzhang(张海斌)
<haibinzhang@...cent.com>
Cc: Jason Wang <jasowang@...hat.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
lidongchen(陈立东) <lidongchen@...cent.com>,
yunfangtai(台运方) <yunfangtai@...cent.com>
Subject: Re: [PATCH] vhost-net: set packet weight of tx polling to 2 * vq size
On Fri, Apr 06, 2018 at 08:22:37AM +0000, haibinzhang(张海斌) wrote:
> handle_tx will delay rx for tens or even hundreds of milliseconds when tx busy
> polling udp packets with small length(e.g. 1byte udp payload), because setting
> VHOST_NET_WEIGHT takes into account only sent-bytes but no single packet length.
>
> Ping-Latencies shown below were tested between two Virtual Machines using
> netperf (UDP_STREAM, len=1), and then another machine pinged the client:
>
> Packet-Weight Ping-Latencies(millisecond)
> min avg max
> Origin 3.319 18.489 57.303
> 64 1.643 2.021 2.552
> 128 1.825 2.600 3.224
> 256 1.997 2.710 4.295
> 512 1.860 3.171 4.631
> 1024 2.002 4.173 9.056
> 2048 2.257 5.650 9.688
> 4096 2.093 8.508 15.943
And this is with Q size 256 right?
> Ring size is a hint from device about a burst size it can tolerate. Based on
> benchmarks, set the weight to 2 * vq size.
>
> To evaluate this change, another tests were done using netperf(RR, TX) between
> two machines with Intel(R) Xeon(R) Gold 6133 CPU @ 2.50GHz, and vq size was
> tweaked through qemu. Results shown below does not show obvious changes.
What I asked for is ping-latency with different VQ sizes,
streaming below does not show anything.
> vq size=256 TCP_RR vq size=512 TCP_RR
> size/sessions/+thu%/+normalize% size/sessions/+thu%/+normalize%
> 1/ 1/ -7%/ -2% 1/ 1/ 0%/ -2%
> 1/ 4/ +1%/ 0% 1/ 4/ +1%/ 0%
> 1/ 8/ +1%/ -2% 1/ 8/ 0%/ +1%
> 64/ 1/ -6%/ 0% 64/ 1/ +7%/ +3%
> 64/ 4/ 0%/ +2% 64/ 4/ -1%/ +1%
> 64/ 8/ 0%/ 0% 64/ 8/ -1%/ -2%
> 256/ 1/ -3%/ -4% 256/ 1/ -4%/ -2%
> 256/ 4/ +3%/ +4% 256/ 4/ +1%/ +2%
> 256/ 8/ +2%/ 0% 256/ 8/ +1%/ -1%
>
> vq size=256 UDP_RR vq size=512 UDP_RR
> size/sessions/+thu%/+normalize% size/sessions/+thu%/+normalize%
> 1/ 1/ -5%/ +1% 1/ 1/ -3%/ -2%
> 1/ 4/ +4%/ +1% 1/ 4/ -2%/ +2%
> 1/ 8/ -1%/ -1% 1/ 8/ -1%/ 0%
> 64/ 1/ -2%/ -3% 64/ 1/ +1%/ +1%
> 64/ 4/ -5%/ -1% 64/ 4/ +2%/ 0%
> 64/ 8/ 0%/ -1% 64/ 8/ -2%/ +1%
> 256/ 1/ +7%/ +1% 256/ 1/ -7%/ 0%
> 256/ 4/ +1%/ +1% 256/ 4/ -3%/ -4%
> 256/ 8/ +2%/ +2% 256/ 8/ +1%/ +1%
>
> vq size=256 TCP_STREAM vq size=512 TCP_STREAM
> size/sessions/+thu%/+normalize% size/sessions/+thu%/+normalize%
> 64/ 1/ 0%/ -3% 64/ 1/ 0%/ 0%
> 64/ 4/ +3%/ -1% 64/ 4/ -2%/ +4%
> 64/ 8/ +9%/ -4% 64/ 8/ -1%/ +2%
> 256/ 1/ +1%/ -4% 256/ 1/ +1%/ +1%
> 256/ 4/ -1%/ -1% 256/ 4/ -3%/ 0%
> 256/ 8/ +7%/ +5% 256/ 8/ -3%/ 0%
> 512/ 1/ +1%/ 0% 512/ 1/ -1%/ -1%
> 512/ 4/ +1%/ -1% 512/ 4/ 0%/ 0%
> 512/ 8/ +7%/ -5% 512/ 8/ +6%/ -1%
> 1024/ 1/ 0%/ -1% 1024/ 1/ 0%/ +1%
> 1024/ 4/ +3%/ 0% 1024/ 4/ +1%/ 0%
> 1024/ 8/ +8%/ +5% 1024/ 8/ -1%/ 0%
> 2048/ 1/ +2%/ +2% 2048/ 1/ -1%/ 0%
> 2048/ 4/ +1%/ 0% 2048/ 4/ 0%/ -1%
> 2048/ 8/ -2%/ 0% 2048/ 8/ 5%/ -1%
> 4096/ 1/ -2%/ 0% 4096/ 1/ -2%/ 0%
> 4096/ 4/ +2%/ 0% 4096/ 4/ 0%/ 0%
> 4096/ 8/ +9%/ -2% 4096/ 8/ -5%/ -1%
>
> Signed-off-by: Haibin Zhang <haibinzhang@...cent.com>
> Signed-off-by: Yunfang Tai <yunfangtai@...cent.com>
> Signed-off-by: Lidong Chen <lidongchen@...cent.com>
Code is fine but I'd like to see validation of the heuristic
2*vq->num with another vq size.
> ---
> drivers/vhost/net.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 8139bc70ad7d..3563a305cc0a 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -44,6 +44,10 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
> * Using this limit prevents one virtqueue from starving others. */
> #define VHOST_NET_WEIGHT 0x80000
>
> +/* Max number of packets transferred before requeueing the job.
> + * Using this limit prevents one virtqueue from starving rx. */
> +#define VHOST_NET_PKT_WEIGHT(vq) ((vq)->num * 2)
> +
> /* MAX number of TX used buffers for outstanding zerocopy */
> #define VHOST_MAX_PEND 128
> #define VHOST_GOODCOPY_LEN 256
> @@ -473,6 +477,7 @@ static void handle_tx(struct vhost_net *net)
> struct socket *sock;
> struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
> bool zcopy, zcopy_used;
> + int sent_pkts = 0;
>
> mutex_lock(&vq->mutex);
> sock = vq->private_data;
> @@ -580,7 +585,8 @@ static void handle_tx(struct vhost_net *net)
> else
> vhost_zerocopy_signal_used(net, vq);
> vhost_net_tx_packet(net);
> - if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
> + if (unlikely(total_len >= VHOST_NET_WEIGHT) ||
> + unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT(vq))) {
> vhost_poll_queue(&vq->poll);
> break;
> }
> --
> 2.12.3
>
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