target/linux/generic/patches-3.2/120-ppp_txqueue_restart.patch

   1 For every transmitted packet, ppp_start_xmit() will stop the netdev
   2 queue and then, if appropriate, restart it. This causes the TX softirq
   3 to run, entirely gratuitously.
   4
   5 This is "only" a waste of CPU time in the normal case, but it's actively
   6 harmful when the PPP device is a TEQL slave — the wakeup will cause the
   7 offending device to receive the next TX packet from the TEQL queue, when
   8 it *should* have gone to the next slave in the list. We end up seeing
   9 large bursts of packets on just *one* slave device, rather than using
  10 the full available bandwidth over all slaves.
  11
  12 This patch fixes the problem by *not* unconditionally stopping the queue
  13 in ppp_start_xmit(). It adds a return value from ppp_xmit_process()
  14 which indicates whether the queue should be stopped or not.
  15
  16 It *doesn't* remove the call to netif_wake_queue() from
  17 ppp_xmit_process(), because other code paths (especially from
  18 ppp_output_wakeup()) need it there and it's messy to push it out to the
  19 other callers to do it based on the return value. So we leave it in
  20 place — it's a no-op in the case where the queue wasn't stopped, so it's
  21 harmless in the TX path.
  22
  23 Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
  24
  25 --- a/drivers/net/ppp/ppp_generic.c~    2012-01-26 00:39:32.000000000 +0000
  26 +++ b/drivers/net/ppp/ppp_generic.c     2012-03-26 10:32:31.286744147 +0100
  27 @@ -235,7 +235,7 @@ struct ppp_net {
  28  /* Prototypes. */
  29  static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
  30                         struct file *file, unsigned int cmd, unsigned long arg);
  31 -static void ppp_xmit_process(struct ppp *ppp);
  32 +static int ppp_xmit_process(struct ppp *ppp);
  33  static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
  34  static void ppp_push(struct ppp *ppp);
  35  static void ppp_channel_push(struct channel *pch);
  36 @@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, stru
  37         proto = npindex_to_proto[npi];
  38         put_unaligned_be16(proto, pp);
  39
  40 -       netif_stop_queue(dev);
  41         skb_queue_tail(&ppp->file.xq, skb);
  42 -       ppp_xmit_process(ppp);
  43 +       if (!ppp_xmit_process(ppp))
  44 +               netif_stop_queue(dev);
  45         return NETDEV_TX_OK;
  46
  47   outf:
  48 @@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device
  49   * Called to do any work queued up on the transmit side
  50   * that can now be done.
  51   */
  52 -static void
  53 +static int
  54  ppp_xmit_process(struct ppp *ppp)
  55  {
  56         struct sk_buff *skb;
  57 +       int ret = 0;
  58
  59         ppp_xmit_lock(ppp);
  60         if (!ppp->closing) {
  61 @@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
  62                         ppp_send_frame(ppp, skb);
  63                 /* If there's no work left to do, tell the core net
  64                    code that we can accept some more. */
  65 -               if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
  66 +               if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
  67                         netif_wake_queue(ppp->dev);
  68 +                       ret = 1;
  69 +               }
  70         }
  71         ppp_xmit_unlock(ppp);
  72 +       return ret;
  73  }
  74
  75  static inline struct sk_buff *
  76
  77 --
  78 David Woodhouse                            Open Source Technology Centre
  79 David.Woodhouse@intel.com                              Intel Corporation
  80
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