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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 <David.Woodhouse@intel.com>
--- a/drivers/net/ppp/ppp_generic.c~ 2012-01-26 00:39:32.000000000 +0000
+++ b/drivers/net/ppp/ppp_generic.c 2012-03-26 10:32:31.286744147 +0100
@@ -235,7 +235,7 @@ struct ppp_net {
/* Prototypes. */
static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
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_push(struct ppp *ppp);
static void ppp_channel_push(struct channel *pch);
@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, stru
proto = npindex_to_proto[npi];
put_unaligned_be16(proto, pp);
- netif_stop_queue(dev);
skb_queue_tail(&ppp->file.xq, skb);
- ppp_xmit_process(ppp);
+ if (!ppp_xmit_process(ppp))
+ netif_stop_queue(dev);
return NETDEV_TX_OK;
outf:
@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device
* Called to do any work queued up on the transmit side
* that can now be done.
*/
-static void
+static int
ppp_xmit_process(struct ppp *ppp)
{
struct sk_buff *skb;
+ int ret = 0;
ppp_xmit_lock(ppp);
if (!ppp->closing) {
@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
ppp_send_frame(ppp, skb);
/* If there's no work left to do, tell the core net
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);
+ ret = 1;
+ }
}
ppp_xmit_unlock(ppp);
+ return ret;
}
static inline struct sk_buff *
--
David Woodhouse Open Source Technology Centre
David.Woodhouse@intel.com Intel Corporation
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