ppp: Fix high softirq utilization with pppoa
Users of the Geos platform are reporting high CPU utilization. This seems to be rooted in a problem with the TX queue restart in PPP. Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com> SVN-Revision: 31096
This commit is contained in:
parent
8de1475a27
commit
af2c5df66a
2 changed files with 164 additions and 0 deletions
|
@ -0,0 +1,82 @@
|
|||
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
|
||||
|
||||
|
||||
|
|
@ -0,0 +1,82 @@
|
|||
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
|
||||
|
||||
|
||||
|
Loading…
Reference in a new issue