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    Subject[ 062/167] [PATCH 02/26] ppp: Dont stop and restart queue on every TX packet
    3.2-stable review patch.  If anyone has any objections, please let me know.


    From: David Woodhouse <>

    [ This combines upstream commit
    e675f0cc9a872fd152edc0c77acfed19bf28b81e and follow-on bug fix
    commit 9a5d2bd99e0dfe9a31b3c160073ac445ba3d773f ]

    For every transmitted packet, ppp_start_xmit() will stop the netdev
    queue and then, if appropriate, restart it. This causes the TX softirq
    to run, entirely gratuitously.

    This is "only" a waste of CPU time in the normal case, but it's actively
    harmful when the PPP device is a TEQL slave — the wakeup will cause the
    offending device to receive the next TX packet from the TEQL queue, when
    it *should* have gone to the next slave in the list. We end up seeing
    large bursts of packets on just *one* slave device, rather than using
    the full available bandwidth over all slaves.

    This patch fixes the problem by *not* unconditionally stopping the queue
    in ppp_start_xmit(). It adds a return value from ppp_xmit_process()
    which indicates whether the queue should be stopped or not.

    It *doesn't* remove the call to netif_wake_queue() from
    ppp_xmit_process(), because other code paths (especially from
    ppp_output_wakeup()) need it there and it's messy to push it out to the
    other callers to do it based on the return value. So we leave it in
    place — it's a no-op in the case where the queue wasn't stopped, so it's
    harmless in the TX path.

    Signed-off-by: David Woodhouse <>
    Signed-off-by: David S. Miller <>
    Signed-off-by: Ben Hutchings <>
    drivers/net/ppp/ppp_generic.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
    index 486b404..3ed983c 100644
    --- a/drivers/net/ppp/ppp_generic.c
    +++ b/drivers/net/ppp/ppp_generic.c
    @@ -968,7 +968,6 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
    proto = npindex_to_proto[npi];
    put_unaligned_be16(proto, pp);

    - netif_stop_queue(dev);
    skb_queue_tail(&ppp->file.xq, skb);
    return NETDEV_TX_OK;
    @@ -1063,6 +1062,8 @@ ppp_xmit_process(struct ppp *ppp)
    code that we can accept some more. */
    if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
    + else
    + netif_stop_queue(ppp->dev);

     \ /
      Last update: 2012-05-09 09:02    [W:0.023 / U:6.556 seconds]
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