diff options
Diffstat (limited to 'target/linux/generic/patches-3.2/130-pppoatm-queue-depth.patch')
| -rw-r--r-- | target/linux/generic/patches-3.2/130-pppoatm-queue-depth.patch | 188 |
1 files changed, 0 insertions, 188 deletions
diff --git a/target/linux/generic/patches-3.2/130-pppoatm-queue-depth.patch b/target/linux/generic/patches-3.2/130-pppoatm-queue-depth.patch deleted file mode 100644 index 247a312290..0000000000 --- a/target/linux/generic/patches-3.2/130-pppoatm-queue-depth.patch +++ /dev/null @@ -1,188 +0,0 @@ -From 9d02daf754238adac48fa075ee79e7edd3d79ed3 Mon Sep 17 00:00:00 2001 -From: David Woodhouse <dwmw2@infradead.org> -Date: Sun, 8 Apr 2012 09:55:43 +0000 -Subject: [PATCH] pppoatm: Fix excessive queue bloat - -We discovered that PPPoATM has an excessively deep transmit queue. A -queue the size of the default socket send buffer (wmem_default) is -maintained between the PPP generic core and the ATM device. - -Fix it to queue a maximum of *two* packets. The one the ATM device is -currently working on, and one more for the ATM driver to process -immediately in its TX done interrupt handler. The PPP core is designed -to feed packets to the channel with minimal latency, so that really -ought to be enough to keep the ATM device busy. - -While we're at it, fix the fact that we were triggering the wakeup -tasklet on *every* pppoatm_pop() call. The comment saying "this is -inefficient, but doing it right is too hard" turns out to be overly -pessimistic... I think :) - -On machines like the Traverse Geos, with a slow Geode CPU and two -high-speed ADSL2+ interfaces, there were reports of extremely high CPU -usage which could partly be attributed to the extra wakeups. - -(The wakeup handling could actually be made a whole lot easier if we - stop checking sk->sk_sndbuf altogether. Given that we now only queue - *two* packets ever, one wonders what the point is. As it is, you could - already deadlock the thing by setting the sk_sndbuf to a value lower - than the MTU of the device, and it'd just block for ever.) - -Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> -Signed-off-by: David S. Miller <davem@davemloft.net> ---- - net/atm/pppoatm.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++----- - 1 files changed, 85 insertions(+), 10 deletions(-) - ---- a/net/atm/pppoatm.c -+++ b/net/atm/pppoatm.c -@@ -62,12 +62,25 @@ struct pppoatm_vcc { - void (*old_pop)(struct atm_vcc *, struct sk_buff *); - /* keep old push/pop for detaching */ - enum pppoatm_encaps encaps; -+ atomic_t inflight; -+ unsigned long blocked; - int flags; /* SC_COMP_PROT - compress protocol */ - struct ppp_channel chan; /* interface to generic ppp layer */ - struct tasklet_struct wakeup_tasklet; - }; - - /* -+ * We want to allow two packets in the queue. The one that's currently in -+ * flight, and *one* queued up ready for the ATM device to send immediately -+ * from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so -+ * inflight == -2 represents an empty queue, -1 one packet, and zero means -+ * there are two packets in the queue. -+ */ -+#define NONE_INFLIGHT -2 -+ -+#define BLOCKED 0 -+ -+/* - * Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol - * ID (0xC021) used in autodetection - */ -@@ -102,16 +115,30 @@ static void pppoatm_wakeup_sender(unsign - static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb) - { - struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc); -+ - pvcc->old_pop(atmvcc, skb); -+ atomic_dec(&pvcc->inflight); -+ - /* -- * We don't really always want to do this since it's -- * really inefficient - it would be much better if we could -- * test if we had actually throttled the generic layer. -- * Unfortunately then there would be a nasty SMP race where -- * we could clear that flag just as we refuse another packet. -- * For now we do the safe thing. -+ * We always used to run the wakeup tasklet unconditionally here, for -+ * fear of race conditions where we clear the BLOCKED flag just as we -+ * refuse another packet in pppoatm_send(). This was quite inefficient. -+ * -+ * In fact it's OK. The PPP core will only ever call pppoatm_send() -+ * while holding the channel->downl lock. And ppp_output_wakeup() as -+ * called by the tasklet will *also* grab that lock. So even if another -+ * CPU is in pppoatm_send() right now, the tasklet isn't going to race -+ * with it. The wakeup *will* happen after the other CPU is safely out -+ * of pppoatm_send() again. -+ * -+ * So if the CPU in pppoatm_send() has already set the BLOCKED bit and -+ * it about to return, that's fine. We trigger a wakeup which will -+ * happen later. And if the CPU in pppoatm_send() *hasn't* set the -+ * BLOCKED bit yet, that's fine too because of the double check in -+ * pppoatm_may_send() which is commented there. - */ -- tasklet_schedule(&pvcc->wakeup_tasklet); -+ if (test_and_clear_bit(BLOCKED, &pvcc->blocked)) -+ tasklet_schedule(&pvcc->wakeup_tasklet); - } - - /* -@@ -184,6 +211,51 @@ error: - ppp_input_error(&pvcc->chan, 0); - } - -+static inline int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size) -+{ -+ /* -+ * It's not clear that we need to bother with using atm_may_send() -+ * to check we don't exceed sk->sk_sndbuf. If userspace sets a -+ * value of sk_sndbuf which is lower than the MTU, we're going to -+ * block for ever. But the code always did that before we introduced -+ * the packet count limit, so... -+ */ -+ if (atm_may_send(pvcc->atmvcc, size) && -+ atomic_inc_not_zero_hint(&pvcc->inflight, NONE_INFLIGHT)) -+ return 1; -+ -+ /* -+ * We use test_and_set_bit() rather than set_bit() here because -+ * we need to ensure there's a memory barrier after it. The bit -+ * *must* be set before we do the atomic_inc() on pvcc->inflight. -+ * There's no smp_mb__after_set_bit(), so it's this or abuse -+ * smp_mb__after_clear_bit(). -+ */ -+ test_and_set_bit(BLOCKED, &pvcc->blocked); -+ -+ /* -+ * We may have raced with pppoatm_pop(). If it ran for the -+ * last packet in the queue, *just* before we set the BLOCKED -+ * bit, then it might never run again and the channel could -+ * remain permanently blocked. Cope with that race by checking -+ * *again*. If it did run in that window, we'll have space on -+ * the queue now and can return success. It's harmless to leave -+ * the BLOCKED flag set, since it's only used as a trigger to -+ * run the wakeup tasklet. Another wakeup will never hurt. -+ * If pppoatm_pop() is running but hasn't got as far as making -+ * space on the queue yet, then it hasn't checked the BLOCKED -+ * flag yet either, so we're safe in that case too. It'll issue -+ * an "immediate" wakeup... where "immediate" actually involves -+ * taking the PPP channel's ->downl lock, which is held by the -+ * code path that calls pppoatm_send(), and is thus going to -+ * wait for us to finish. -+ */ -+ if (atm_may_send(pvcc->atmvcc, size) && -+ atomic_inc_not_zero(&pvcc->inflight)) -+ return 1; -+ -+ return 0; -+} - /* - * Called by the ppp_generic.c to send a packet - returns true if packet - * was accepted. If we return false, then it's our job to call -@@ -207,7 +279,7 @@ static int pppoatm_send(struct ppp_chann - struct sk_buff *n; - n = skb_realloc_headroom(skb, LLC_LEN); - if (n != NULL && -- !atm_may_send(pvcc->atmvcc, n->truesize)) { -+ !pppoatm_may_send(pvcc, n->truesize)) { - kfree_skb(n); - goto nospace; - } -@@ -215,12 +287,12 @@ static int pppoatm_send(struct ppp_chann - skb = n; - if (skb == NULL) - return DROP_PACKET; -- } else if (!atm_may_send(pvcc->atmvcc, skb->truesize)) -+ } else if (!pppoatm_may_send(pvcc, skb->truesize)) - goto nospace; - memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN); - break; - case e_vc: -- if (!atm_may_send(pvcc->atmvcc, skb->truesize)) -+ if (!pppoatm_may_send(pvcc, skb->truesize)) - goto nospace; - break; - case e_autodetect: -@@ -285,6 +357,9 @@ static int pppoatm_assign_vcc(struct atm - if (pvcc == NULL) - return -ENOMEM; - pvcc->atmvcc = atmvcc; -+ -+ /* Maximum is zero, so that we can use atomic_inc_not_zero() */ -+ atomic_set(&pvcc->inflight, NONE_INFLIGHT); - pvcc->old_push = atmvcc->push; - pvcc->old_pop = atmvcc->pop; - pvcc->encaps = (enum pppoatm_encaps) be.encaps; |