From: "Wiles, Keith" <keith.wiles@intel.com>
To: "Michał Mirosław" <mirqus@gmail.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"pmatilai@redhat.com" <pmatilai@redhat.com>,
"yuanhan.liu@linux.intel.com" <yuanhan.liu@linux.intel.com>
Subject: Re: [dpdk-dev] [PATCH v4] drivers/net:new PMD using tun/tap host interface
Date: Tue, 11 Oct 2016 20:56:28 +0000 [thread overview]
Message-ID: <0685C9CE-94DC-43E4-A34B-17912E51B5ED@intel.com> (raw)
In-Reply-To: <CAHXqBFJsMsHqKD-dsS=DUg5DXwcjBc9T6=wuHft5utO3cgj0Ug@mail.gmail.com>
Regards,
Keith
> On Oct 11, 2016, at 6:30 AM, Michał Mirosław <mirqus@gmail.com> wrote:
>
> 2016-10-04 16:45 GMT+02:00, Keith Wiles <keith.wiles@intel.com>:
>> The rte_eth_tap.c PMD creates a device using TUN/TAP interfaces
>> on the local host. The PMD allows for DPDK and the host to
>> communicate using a raw device interface on the host and in
>> the DPDK application. The device created is a Tap device with
>> a L2 packet header.
> [...]
>> +static uint16_t
>> +pmd_rx_burst(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
>> +{
>> + int len, n;
>> + struct rte_mbuf *mbuf;
>> + struct rx_queue *rxq = queue;
>> + struct pollfd pfd;
>> + uint16_t num_rx;
>> + unsigned long num_rx_bytes = 0;
>> +
>> + pfd.events = POLLIN;
>> + pfd.fd = rxq->fd;
>> + for (num_rx = 0; num_rx < nb_pkts; ) {
>> + n = poll(&pfd, 1, 0);
>> +
>> + if (n <= 0)
>> + break;
>> +
>
> Considering that syscalls are rather expensive, it would be cheaper to
> allocate an mbuf here and free it when read() returns -1 instead of
> calling poll() to check whether a packet is waiting. This way you
> save a syscall per packet and replace one syscall with one mbuf free
> per poll.
I made this change, but saw no performance difference in the two methods. Removing poll seems reasonable as it is simpler. TAP is already so slow is why the performance did not change is my guess. Anyone wanting to use TAP as a high performance interface is going to be surprised. I believe the best use case for the TAP interface is for control or exception path.
>
> Best Regards,
> Michał Mirosław
next prev parent reply other threads:[~2016-10-11 20:56 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-15 14:10 [dpdk-dev] [PATCH 1/3] " Keith Wiles
2016-09-15 14:10 ` [dpdk-dev] [PATCH 2/3] docs:tun/tap PMD information Keith Wiles
2016-09-15 14:13 ` Wiles, Keith
2016-09-15 14:15 ` Wiles, Keith
2016-09-21 2:00 ` [dpdk-dev] [PATCH v3] drivers/net:new PMD using tun/tap host interface Keith Wiles
2016-10-04 14:45 ` [dpdk-dev] [PATCH v4] " Keith Wiles
2016-10-11 9:40 ` Ferruh Yigit
2016-10-11 11:30 ` Michał Mirosław
2016-10-11 20:56 ` Wiles, Keith [this message]
2016-10-12 8:14 ` Michał Mirosław
2016-10-11 11:49 ` Ferruh Yigit
2016-10-11 21:07 ` Wiles, Keith
2016-10-11 12:28 ` Ferruh Yigit
2016-10-11 20:57 ` Wiles, Keith
2016-10-11 21:51 ` [dpdk-dev] [PATCH v5] " Keith Wiles
2016-10-12 14:56 ` Ferruh Yigit
2016-10-12 18:19 ` Wiles, Keith
2016-10-12 19:57 ` Wiles, Keith
2016-10-12 20:54 ` [dpdk-dev] [PATCH v6] " Keith Wiles
2016-10-13 14:41 ` Ferruh Yigit
2016-10-13 15:36 ` [dpdk-dev] [PATCH v7] " Keith Wiles
2016-10-13 16:11 ` [dpdk-dev] [PATCH v8] " Keith Wiles
2016-10-13 16:33 ` Mcnamara, John
2016-10-13 22:03 ` [dpdk-dev] [PATCH v9] " Keith Wiles
2016-10-14 6:41 ` Mcnamara, John
2016-10-14 9:39 ` Ferruh Yigit
2016-11-21 12:56 ` Ferruh Yigit
2016-11-25 19:38 ` Aws Ismail
2016-11-29 21:36 ` Aws Ismail
2016-11-29 22:16 ` Wiles, Keith
2016-12-07 19:38 ` [dpdk-dev] [PATCH v10] drivers/net:new TUN/TAP device PMD Keith Wiles
2016-12-07 20:15 ` Aws Ismail
2016-12-09 18:16 ` Ferruh Yigit
2016-12-09 19:05 ` [dpdk-dev] [PATCH v11] " Keith Wiles
2016-12-12 12:39 ` Vasily Philipov
2016-12-12 14:24 ` [dpdk-dev] [PATCH v12] net/tap: new " Keith Wiles
2016-12-12 14:38 ` Keith Wiles
2016-12-12 19:13 ` Marc
2016-12-12 21:09 ` Wiles, Keith
2016-12-13 13:54 ` Ferruh Yigit
2017-01-20 12:14 ` Ferruh Yigit
2017-01-20 14:25 ` [dpdk-dev] [PATCH] net/tap: fix IFF_MULTI_QUEUE in older kernels not found Keith Wiles
2017-01-20 14:30 ` Keith Wiles
2017-01-20 16:11 ` Ferruh Yigit
2017-01-20 17:37 ` Thomas Monjalon
2016-09-15 14:10 ` [dpdk-dev] [PATCH 3/3] drivers/net:build support for new tap device driver Keith Wiles
2016-09-16 7:36 ` Panu Matilainen
2016-09-16 14:46 ` Wiles, Keith
2016-09-16 16:22 ` [dpdk-dev] [PATCH v2] drivers/net:new PMD using tun/tap host interface Keith Wiles
2016-09-18 13:25 ` Yuanhan Liu
2016-09-18 16:20 ` Wiles, Keith
2016-09-19 0:29 ` Yuanhan Liu
2016-09-19 15:56 ` Wiles, Keith
2016-09-20 3:54 ` Yuanhan Liu
2016-09-20 4:05 ` Yuanhan Liu
2016-09-21 1:32 ` Wiles, Keith
2016-09-21 2:13 ` Yuanhan Liu
2016-09-21 8:24 ` Thomas Monjalon
2016-09-21 23:55 ` Wiles, Keith
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