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From: Bev SCHWARTZ <bev.schwartz@raytheon.com>
To: "users@dpdk.org" <users@dpdk.org>
Subject: [dpdk-users] Significant performance degradation when using tx buffers rather than rte_eth_tx_burst
Date: Wed, 8 Jul 2020 17:23:01 +0000
Message-ID: <DM3P110MB0524688C02177E5864CEB384EA670@DM3P110MB0524.NAMP110.PROD.OUTLOOK.COM> (raw)

I am writing a bridge using DPDK, where I have traffic read from one port transmitted to the other.  Here is the core of the program, based on basicfwd.c.

while (!force_quit) {
    nb_rx = rte_eth_rx_burst(rx_port, rx_queue, bufs, BURST_SIZE);
    for (i = 0; i < nb_rx; i++) {
        /* inspect packet */
    }
    nb_tx = rte_eth_tx_burst(tx_port, tx_queue, bufs, nb_rx);
    for (i = nb_tx; i < nb_rx; i++) {
        rte_pktmbuf_free(bufs[i]);
    }
}

(A bunch of error checking and such left out for brevity.)

This worked great, I got bandwidth equivalent to using a Linux Bridge.

I then tried using tx buffers instead.  (Initialization code left out for brevity.)  Here is the new loop.

while (!force_quit) {
    nb_rx = rte_eth_rx_burst(rx_port, rx_queue, bufs, BURST_SIZE);
    for (i = 0; i < nb_rx; i++) {
        /* inspect packet */
        rte_eth_tx_buffer(tx_port, tx_queue, tx_buffer, bufs[i]);
    }
    rte_eth_tx_buffer_flush(tx_port, tx_queue, tx_buffer);
}

(Once again, error checking left out for brevity.)

I am running this on 8 cores, each core has its own loop.  (tx_buffer is created for each core.)

If I have well balanced traffic across the cores, then my performance goes down, about 5% or so.  If I have unbalanced traffic such as all traffic coming from a single flow, my performance goes down 80% from about 10 gbs to 2gbs.

I want to stress that the ONLY thing that changed in this code is changing how I transmit packets.  Everything else is the same.

Any idea why this would cause such a degradation in bit rate?

-Bev

             reply	other threads:[~2020-07-08 17:23 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-08 17:23 Bev SCHWARTZ [this message]
2020-07-08 20:42 ` Suraj R Gupta
2020-07-13  6:32   ` Manish Kumar
2020-07-13 17:18     ` Bev SCHWARTZ

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