Commit e675f0cc authored by David Woodhouse's avatar David Woodhouse Committed by David S. Miller

ppp: Don't stop and restart queue on every TX packet

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: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2def16ae
...@@ -235,7 +235,7 @@ struct ppp_net { ...@@ -235,7 +235,7 @@ struct ppp_net {
/* Prototypes. */ /* Prototypes. */
static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf, static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
struct file *file, unsigned int cmd, unsigned long arg); struct file *file, unsigned int cmd, unsigned long arg);
static void ppp_xmit_process(struct ppp *ppp); static int ppp_xmit_process(struct ppp *ppp);
static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb); static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
static void ppp_push(struct ppp *ppp); static void ppp_push(struct ppp *ppp);
static void ppp_channel_push(struct channel *pch); static void ppp_channel_push(struct channel *pch);
...@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev) ...@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
proto = npindex_to_proto[npi]; proto = npindex_to_proto[npi];
put_unaligned_be16(proto, pp); put_unaligned_be16(proto, pp);
netif_stop_queue(dev);
skb_queue_tail(&ppp->file.xq, skb); skb_queue_tail(&ppp->file.xq, skb);
ppp_xmit_process(ppp); if (!ppp_xmit_process(ppp))
netif_stop_queue(dev);
return NETDEV_TX_OK; return NETDEV_TX_OK;
outf: outf:
...@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device *dev) ...@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device *dev)
* Called to do any work queued up on the transmit side * Called to do any work queued up on the transmit side
* that can now be done. * that can now be done.
*/ */
static void static int
ppp_xmit_process(struct ppp *ppp) ppp_xmit_process(struct ppp *ppp)
{ {
struct sk_buff *skb; struct sk_buff *skb;
int ret = 0;
ppp_xmit_lock(ppp); ppp_xmit_lock(ppp);
if (!ppp->closing) { if (!ppp->closing) {
...@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp) ...@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
ppp_send_frame(ppp, skb); ppp_send_frame(ppp, skb);
/* If there's no work left to do, tell the core net /* If there's no work left to do, tell the core net
code that we can accept some more. */ code that we can accept some more. */
if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
netif_wake_queue(ppp->dev); netif_wake_queue(ppp->dev);
ret = 1;
}
} }
ppp_xmit_unlock(ppp); ppp_xmit_unlock(ppp);
return ret;
} }
static inline struct sk_buff * static inline struct sk_buff *
......
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