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:
Florian Fainelli
@@ -0,0 +1,82 @@
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For every transmitted packet, ppp_start_xmit() will stop the netdev
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queue and then, if appropriate, restart it. This causes the TX softirq
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to run, entirely gratuitously.
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This is "only" a waste of CPU time in the normal case, but it's actively
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harmful when the PPP device is a TEQL slave — the wakeup will cause the
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offending device to receive the next TX packet from the TEQL queue, when
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it *should* have gone to the next slave in the list. We end up seeing
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large bursts of packets on just *one* slave device, rather than using
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the full available bandwidth over all slaves.
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This patch fixes the problem by *not* unconditionally stopping the queue
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in ppp_start_xmit(). It adds a return value from ppp_xmit_process()
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which indicates whether the queue should be stopped or not.
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It *doesn't* remove the call to netif_wake_queue() from
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ppp_xmit_process(), because other code paths (especially from
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ppp_output_wakeup()) need it there and it's messy to push it out to the
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other callers to do it based on the return value. So we leave it in
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place — it's a no-op in the case where the queue wasn't stopped, so it's
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harmless in the TX path.
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Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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--- a/drivers/net/ppp/ppp_generic.c~ 2012-01-26 00:39:32.000000000 +0000
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+++ b/drivers/net/ppp/ppp_generic.c 2012-03-26 10:32:31.286744147 +0100
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@@ -235,7 +235,7 @@ struct ppp_net {
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/* Prototypes. */
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static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
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struct file *file, unsigned int cmd, unsigned long arg);
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-static void ppp_xmit_process(struct ppp *ppp);
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+static int ppp_xmit_process(struct ppp *ppp);
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static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
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static void ppp_push(struct ppp *ppp);
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static void ppp_channel_push(struct channel *pch);
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@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, stru
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proto = npindex_to_proto[npi];
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put_unaligned_be16(proto, pp);
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- netif_stop_queue(dev);
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skb_queue_tail(&ppp->file.xq, skb);
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- ppp_xmit_process(ppp);
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+ if (!ppp_xmit_process(ppp))
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+ netif_stop_queue(dev);
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return NETDEV_TX_OK;
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outf:
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@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device
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* Called to do any work queued up on the transmit side
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* that can now be done.
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*/
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-static void
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+static int
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ppp_xmit_process(struct ppp *ppp)
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{
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struct sk_buff *skb;
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+ int ret = 0;
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ppp_xmit_lock(ppp);
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if (!ppp->closing) {
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@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
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ppp_send_frame(ppp, skb);
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/* If there's no work left to do, tell the core net
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code that we can accept some more. */
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- if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
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+ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
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netif_wake_queue(ppp->dev);
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+ ret = 1;
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+ }
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}
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ppp_xmit_unlock(ppp);
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+ return ret;
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}
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static inline struct sk_buff *
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--
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David Woodhouse Open Source Technology Centre
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David.Woodhouse@intel.com Intel Corporation
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@@ -0,0 +1,82 @@
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For every transmitted packet, ppp_start_xmit() will stop the netdev
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queue and then, if appropriate, restart it. This causes the TX softirq
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to run, entirely gratuitously.
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This is "only" a waste of CPU time in the normal case, but it's actively
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harmful when the PPP device is a TEQL slave — the wakeup will cause the
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offending device to receive the next TX packet from the TEQL queue, when
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it *should* have gone to the next slave in the list. We end up seeing
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large bursts of packets on just *one* slave device, rather than using
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the full available bandwidth over all slaves.
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This patch fixes the problem by *not* unconditionally stopping the queue
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in ppp_start_xmit(). It adds a return value from ppp_xmit_process()
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which indicates whether the queue should be stopped or not.
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It *doesn't* remove the call to netif_wake_queue() from
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ppp_xmit_process(), because other code paths (especially from
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ppp_output_wakeup()) need it there and it's messy to push it out to the
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other callers to do it based on the return value. So we leave it in
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place — it's a no-op in the case where the queue wasn't stopped, so it's
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harmless in the TX path.
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Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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--- a/drivers/net/ppp/ppp_generic.c~ 2012-01-26 00:39:32.000000000 +0000
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+++ b/drivers/net/ppp/ppp_generic.c 2012-03-26 10:32:31.286744147 +0100
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@@ -235,7 +235,7 @@ struct ppp_net {
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/* Prototypes. */
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static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
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struct file *file, unsigned int cmd, unsigned long arg);
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-static void ppp_xmit_process(struct ppp *ppp);
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+static int ppp_xmit_process(struct ppp *ppp);
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static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
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static void ppp_push(struct ppp *ppp);
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static void ppp_channel_push(struct channel *pch);
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@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, stru
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proto = npindex_to_proto[npi];
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put_unaligned_be16(proto, pp);
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- netif_stop_queue(dev);
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skb_queue_tail(&ppp->file.xq, skb);
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- ppp_xmit_process(ppp);
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+ if (!ppp_xmit_process(ppp))
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+ netif_stop_queue(dev);
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return NETDEV_TX_OK;
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outf:
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@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device
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* Called to do any work queued up on the transmit side
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* that can now be done.
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*/
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-static void
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+static int
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ppp_xmit_process(struct ppp *ppp)
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{
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struct sk_buff *skb;
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+ int ret = 0;
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ppp_xmit_lock(ppp);
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if (!ppp->closing) {
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@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
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ppp_send_frame(ppp, skb);
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/* If there's no work left to do, tell the core net
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code that we can accept some more. */
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- if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
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+ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
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netif_wake_queue(ppp->dev);
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+ ret = 1;
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+ }
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}
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ppp_xmit_unlock(ppp);
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+ return ret;
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}
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static inline struct sk_buff *
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--
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David Woodhouse Open Source Technology Centre
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David.Woodhouse@intel.com Intel Corporation
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