• Bernd Eckstein's avatar
    usbnet: ipheth: fix racing condition · 94d250fa
    Bernd Eckstein authored
    Fix a racing condition in ipheth.c that can lead to slow performance.
    
    Bug: In ipheth_tx(), netif_wake_queue() may be called on the callback
    ipheth_sndbulk_callback(), _before_ netif_stop_queue() is called.
    When this happens, the queue is stopped longer than it needs to be,
    thus reducing network performance.
    
    Fix: Move netif_stop_queue() in front of usb_submit_urb(). Now the order
    is always correct. In case, usb_submit_urb() fails, the queue is woken up
    again as callback will not fire.
    
    Testing: This racing condition is usually not noticeable, as it has to
    occur very frequently to slowdown the network. The callback from the USB
    is usually triggered slow enough, so the situation does not appear.
    However, on a Ubuntu Linux on VMWare Workstation, running on Windows 10,
    the we loose the race quite often and the following speedup can be noticed:
    
    Without this patch: Download:  4.10 Mbit/s, Upload:  4.01 Mbit/s
    With this patch:    Download: 36.23 Mbit/s, Upload: 17.61 Mbit/s
    Signed-off-by: default avatarOliver Zweigle <Oliver.Zweigle@faro.com>
    Signed-off-by: default avatarBernd Eckstein <3ernd.Eckstein@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    94d250fa
ipheth.c 14 KB