RE: [PATCH] make tg3 NAPI support configurable

Hi all,

I found that testing if any tx work is done in dev->poll before exiting 
polled mode improves performance by about 7% (max) in a 2-port e100 bridge
forwarding unidirectional test case. If tx work is not considered when 
deciding whether to netif_rx_complete, the transmitting interface sees 
loads of interrupts and hence forwarding throughput is degraded. 

When testing with bidirectional test data, no improvement is seen since 
the dev->poll is kept in polled mode on both interfaces due to
receive work.

Hope this helps.

-jc   

quoted

quoted

 Furthermore NAPI can be extended to schedule dev->poll even for TX-
 interrupts. There is pacth for e1000 doing this. We see about 5-8% 
 overall system packet improvement with this.

quoted

I was thinking of a variant JC [jchapman@katalix.com]
mentioned on this list some time ago. He also sent me
the patch for e1000. A test and the patch is below.

JC contributed almost the exact patch for the e100 rewrite and it did
help Tx, but I don't remember how much.  JC, do you remember?  Here is
the snippet:

static int e100_poll(struct net_device *netdev, int *budget)
{
        struct nic *nic = netdev->priv;
        unsigned int work_to_do = min(netdev->quota, *budget);
        unsigned int work_done = 0;
        int tx_cleaned;

        e100_rx_clean(nic, &work_done, work_to_do);
        tx_cleaned = e100_tx_clean(nic);

        /* If no Rx and Tx cleanup work was done, exit polling mode. */
        if((!tx_cleaned && (work_done == 0)) || !netif_running(netdev))
        {
                netif_rx_complete(netdev);
                e100_enable_irq(nic);
                return 0;
        }

        *budget -= work_done;
        netdev->quota -= work_done;

        return 1;
}

 




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