• David Woodhouse's avatar
    pppoatm: Fix excessive queue bloat · 9d02daf7
    David Woodhouse authored
    We discovered that PPPoATM has an excessively deep transmit queue. A
    queue the size of the default socket send buffer (wmem_default) is
    maintained between the PPP generic core and the ATM device.
    Fix it to queue a maximum of *two* packets. The one the ATM device is
    currently working on, and one more for the ATM driver to process
    immediately in its TX done interrupt handler. The PPP core is designed
    to feed packets to the channel with minimal latency, so that really
    ought to be enough to keep the ATM device busy.
    While we're at it, fix the fact that we were triggering the wakeup
    tasklet on *every* pppoatm_pop() call. The comment saying "this is
    inefficient, but doing it right is too hard" turns out to be overly
    pessimistic... I think :)
    On machines like the Traverse Geos, with a slow Geode CPU and two
    high-speed ADSL2+ interfaces, there were reports of extremely high CPU
    usage which could partly be attributed to the extra wakeups.
    (The wakeup handling could actually be made a whole lot easier if we
     stop checking sk->sk_sndbuf altogether. Given that we now only queue
     *two* packets ever, one wonders what the point is. As it is, you could
     already deadlock the thing by setting the sk_sndbuf to a value lower
     than the MTU of the device, and it'd just block for ever.)
    Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
pppoatm.c 13.9 KB