From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>, dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 6/6] examples/vhost: add an option to enable Tx zero copy
Date: Tue, 23 Aug 2016 16:14:44 +0200 [thread overview]
Message-ID: <373f1d24-f5a5-eed1-e342-87fc6c7cc3cb@redhat.com> (raw)
In-Reply-To: <1471939839-29778-7-git-send-email-yuanhan.liu@linux.intel.com>
On 08/23/2016 10:10 AM, Yuanhan Liu wrote:
> Add an option, --tx-zero-copy, to enable Tx zero copy.
>
> One thing worth noting while using Tx zero copy is the nb_tx_desc has
> to be small enough so that the eth driver will hit the mbuf free
> threshold easily and thus free mbuf more frequently.
>
> The reason behind that is, when Tx zero copy is enabled, guest Tx used
> vring will be updated only when corresponding mbuf is freed. If mbuf is
> not freed frequently, the guest Tx vring could be starved.
>
> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> ---
> examples/vhost/main.c | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> index 9974f0b..e3437ad 100644
> --- a/examples/vhost/main.c
> +++ b/examples/vhost/main.c
> @@ -130,6 +130,7 @@ static uint32_t enable_tx_csum;
> static uint32_t enable_tso;
>
> static int client_mode;
> +static int tx_zero_copy;
>
> /* Specify timeout (in useconds) between retries on RX. */
> static uint32_t burst_rx_delay_time = BURST_RX_WAIT_US;
> @@ -297,6 +298,17 @@ port_init(uint8_t port)
>
> rx_ring_size = RTE_TEST_RX_DESC_DEFAULT;
> tx_ring_size = RTE_TEST_TX_DESC_DEFAULT;
> +
> + /*
> + * When Tx zero copy is enabled, guest Tx used vring will be updated
> + * only when corresponding mbuf is freed. Thus, the nb_tx_desc
> + * (tx_ring_size here) must be small enough so that the driver will
> + * hit the free threshold easily and free mbufs timely. Otherwise,
> + * guest Tx vring would be starved.
> + */
> + if (tx_zero_copy)
> + tx_ring_size = 64;
I have a concern about more complex applications, where the mbufs might
not be consumed sequentially.
If one mbuf gets stuck for a while, whereas all others are consumed,
we would face starvation.
For example, the packet is to be routed to a VM, which is paused,
and the routing thread keeps retrying to enqueue the packet for a while.
Anyway, this feature is optional and off by default, so having the
feature applied is not a blocker.
Thanks!
Maxime
next prev parent reply other threads:[~2016-08-23 14:14 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-23 8:10 [dpdk-dev] [PATCH 0/6] vhost: add Tx zero copy support Yuanhan Liu
2016-08-23 8:10 ` [dpdk-dev] [PATCH 1/6] vhost: simplify memory regions handling Yuanhan Liu
2016-08-23 9:17 ` Maxime Coquelin
2016-08-24 7:26 ` Xu, Qian Q
2016-08-24 7:40 ` Yuanhan Liu
2016-08-24 7:36 ` Xu, Qian Q
2016-08-23 8:10 ` [dpdk-dev] [PATCH 2/6] vhost: get guest/host physical address mappings Yuanhan Liu
2016-08-23 9:58 ` Maxime Coquelin
2016-08-23 12:32 ` Yuanhan Liu
2016-08-23 13:25 ` Maxime Coquelin
2016-08-23 13:49 ` Yuanhan Liu
2016-08-23 14:05 ` Maxime Coquelin
2016-08-23 8:10 ` [dpdk-dev] [PATCH 3/6] vhost: introduce last avail idx for Tx Yuanhan Liu
2016-08-23 12:27 ` Maxime Coquelin
2016-08-23 8:10 ` [dpdk-dev] [PATCH 4/6] vhost: add Tx zero copy Yuanhan Liu
2016-08-23 14:04 ` Maxime Coquelin
2016-08-23 14:31 ` Yuanhan Liu
2016-08-23 15:40 ` Maxime Coquelin
2016-08-23 8:10 ` [dpdk-dev] [PATCH 5/6] vhost: add a flag to enable " Yuanhan Liu
2016-09-06 9:00 ` Xu, Qian Q
2016-09-06 9:42 ` Xu, Qian Q
2016-09-06 10:02 ` Yuanhan Liu
2016-09-07 2:43 ` Xu, Qian Q
2016-09-06 9:55 ` Yuanhan Liu
2016-09-07 16:00 ` Thomas Monjalon
2016-09-08 7:21 ` Yuanhan Liu
2016-09-08 7:57 ` Thomas Monjalon
2016-08-23 8:10 ` [dpdk-dev] [PATCH 6/6] examples/vhost: add an option " Yuanhan Liu
2016-08-23 9:31 ` Thomas Monjalon
2016-08-23 12:33 ` Yuanhan Liu
2016-08-23 14:14 ` Maxime Coquelin [this message]
2016-08-23 14:45 ` Yuanhan Liu
2016-08-23 14:18 ` [dpdk-dev] [PATCH 0/6] vhost: add Tx zero copy support Maxime Coquelin
2016-08-23 14:42 ` Yuanhan Liu
2016-08-23 14:53 ` Yuanhan Liu
2016-08-23 16:41 ` Maxime Coquelin
2016-08-29 8:32 ` Xu, Qian Q
2016-08-29 8:57 ` Xu, Qian Q
2016-09-23 4:11 ` Yuanhan Liu
2016-10-09 15:20 ` Yuanhan Liu
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 0/7] vhost: add dequeue " Yuanhan Liu
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 1/7] vhost: simplify memory regions handling Yuanhan Liu
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 2/7] vhost: get guest/host physical address mappings Yuanhan Liu
2016-09-26 20:17 ` Maxime Coquelin
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 3/7] vhost: introduce last avail idx for dequeue Yuanhan Liu
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 4/7] vhost: add dequeue zero copy Yuanhan Liu
2016-09-26 20:45 ` Maxime Coquelin
2016-10-06 14:37 ` Xu, Qian Q
2016-10-09 2:03 ` Yuanhan Liu
2016-10-10 10:12 ` Xu, Qian Q
2016-10-10 10:14 ` Maxime Coquelin
2016-10-10 10:22 ` Xu, Qian Q
2016-10-10 10:40 ` Xu, Qian Q
2016-10-10 11:48 ` Maxime Coquelin
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 5/7] vhost: add a flag to enable " Yuanhan Liu
2016-09-26 20:57 ` Maxime Coquelin
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 6/7] examples/vhost: add an option " Yuanhan Liu
2016-09-26 21:05 ` Maxime Coquelin
2016-09-23 4:13 ` [dpdk-dev] [PATCH v2 7/7] net/vhost: " Yuanhan Liu
2016-09-26 21:05 ` Maxime Coquelin
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 0/7] vhost: add dequeue zero copy support Yuanhan Liu
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 1/7] vhost: simplify memory regions handling Yuanhan Liu
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 2/7] vhost: get guest/host physical address mappings Yuanhan Liu
2016-11-29 3:10 ` linhaifeng
2016-11-29 13:14 ` linhaifeng
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 3/7] vhost: introduce last avail idx for dequeue Yuanhan Liu
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 4/7] vhost: add dequeue zero copy Yuanhan Liu
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 5/7] vhost: add a flag to enable " Yuanhan Liu
2016-10-09 7:27 ` [dpdk-dev] [PATCH v3 6/7] examples/vhost: add an option " Yuanhan Liu
2016-10-09 7:28 ` [dpdk-dev] [PATCH v3 7/7] net/vhost: " Yuanhan Liu
2016-10-11 13:04 ` [dpdk-dev] [PATCH v3 0/7] vhost: add dequeue zero copy support Xu, Qian Q
2016-10-12 7:48 ` Yuanhan Liu
2016-10-09 10:46 ` [dpdk-dev] [PATCH 0/6] vhost: add Tx " linhaifeng
2016-10-10 8:03 ` Yuanhan Liu
2016-10-14 7:30 ` linhaifeng
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