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Date: Sun, 20 Feb 2011 11:36:10 +0100
From: Jiri Pirko <jpirko@...hat.com>
To: Nicolas de Pesloüan
<nicolas.2p.debian@...il.com>
Cc: Jay Vosburgh <fubar@...ibm.com>,
David Miller <davem@...emloft.net>, kaber@...sh.net,
eric.dumazet@...il.com, netdev@...r.kernel.org,
shemminger@...ux-foundation.org, andy@...yhouse.net
Subject: Re: [patch net-next-2.6 V3] net: convert bonding to use rx_handler
Sat, Feb 19, 2011 at 09:27:37PM CET, nicolas.2p.debian@...il.com wrote:
>Le 19/02/2011 14:46, Jiri Pirko a écrit :
>>Sat, Feb 19, 2011 at 02:18:00PM CET, nicolas.2p.debian@...il.com wrote:
>>>Le 19/02/2011 12:28, Jiri Pirko a écrit :
>>>>Sat, Feb 19, 2011 at 12:08:31PM CET, jpirko@...hat.com wrote:
>>>>>Sat, Feb 19, 2011 at 11:56:23AM CET, nicolas.2p.debian@...il.com wrote:
>>>>>>Le 19/02/2011 09:05, Jiri Pirko a écrit :
>>>>>>>This patch converts bonding to use rx_handler. Results in cleaner
>>>>>>>__netif_receive_skb() with much less exceptions needed. Also
>>>>>>>bond-specific work is moved into bond code.
>>>>>>>
>>>>>>>Signed-off-by: Jiri Pirko<jpirko@...hat.com>
>>>>>>>
>>>>>>>v1->v2:
>>>>>>> using skb_iif instead of new input_dev to remember original
>>>>>>> device
>>>>>>>v2->v3:
>>>>>>> set orig_dev = skb->dev if skb_iif is set
>>>>>>>
>>>>>>
>>>>>>Why do we need to let the rx_handlers call netif_rx() or __netif_receive_skb()?
>>>>>>
>>>>>>Bonding used to be handled with very few overhead, simply replacing
>>>>>>skb->dev with skb->dev->master. Time has passed and we eventually
>>>>>>added many special processing for bonding into __netif_receive_skb(),
>>>>>>but the overhead remained very light.
>>>>>>
>>>>>>Calling netif_rx() (or __netif_receive_skb()) to allow nesting would probably lead to some overhead.
>>>>>>
>>>>>>Can't we, instead, loop inside __netif_receive_skb(), and deliver
>>>>>>whatever need to be delivered, to whoever need, inside the loop ?
>>>>>>
>>>>>>rx_handler = rcu_dereference(skb->dev->rx_handler);
>>>>>>while (rx_handler) {
>>>>>> /* ... */
>>>>>> orig_dev = skb->dev;
>>>>>> skb = rx_handler(skb);
>>>>>> /* ... */
>>>>>> rx_handler = (skb->dev != orig_dev) ? rcu_dereference(skb->dev->rx_handler) : NULL;
>>>>>>}
>>>>>>
>>>>>>This would reduce the overhead, while still allowing nesting: vlan on
>>>>>>top on bonding, bridge on top on bonding, ...
>>>>>
>>>>>I see your point. Makes sense to me. But the loop would have to include
>>>>>at least processing of ptype_all too. I'm going to cook a follow-up
>>>>>patch.
>>>>>
>>>>
>>>>DRAFT (doesn't modify rx_handlers):
>>>>
>>>>diff --git a/net/core/dev.c b/net/core/dev.c
>>>>index 4ebf7fe..e5dba47 100644
>>>>--- a/net/core/dev.c
>>>>+++ b/net/core/dev.c
>>>>@@ -3115,6 +3115,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
>>>> {
>>>> struct packet_type *ptype, *pt_prev;
>>>> rx_handler_func_t *rx_handler;
>>>>+ struct net_device *dev;
>>>> struct net_device *orig_dev;
>>>> struct net_device *null_or_dev;
>>>> int ret = NET_RX_DROP;
>>>>@@ -3129,7 +3130,9 @@ static int __netif_receive_skb(struct sk_buff *skb)
>>>> if (netpoll_receive_skb(skb))
>>>> return NET_RX_DROP;
>>>>
>>>>- __this_cpu_inc(softnet_data.processed);
>>>>+ skb->skb_iif = skb->dev->ifindex;
>>>>+ orig_dev = skb->dev;
>>>
>>>orig_dev should be set inside the loop, to reflect "previously
>>>crossed device", while following the path:
>>>
>>>eth0 -> bond0 -> br0.
>>>
>>>First step inside loop:
>>>
>>>orig_dev = eth0
>>>skb->dev = bond0 (at the end of the loop).
>>>
>>>Second step inside loop:
>>>
>>>orig_dev = bond0
>>>skb->dev = br0 (et the end of the loop).
>>>
>>>This would allow for exact match delivery to bond0 if someone bind there.
>>>
>>>>+
>>>> skb_reset_network_header(skb);
>>>> skb_reset_transport_header(skb);
>>>> skb->mac_len = skb->network_header - skb->mac_header;
>>>>@@ -3138,12 +3141,9 @@ static int __netif_receive_skb(struct sk_buff *skb)
>>>>
>>>> rcu_read_lock();
>>>>
>>>>- if (!skb->skb_iif) {
>>>>- skb->skb_iif = skb->dev->ifindex;
>>>>- orig_dev = skb->dev;
>>>>- } else {
>>>>- orig_dev = dev_get_by_index_rcu(dev_net(skb->dev), skb->skb_iif);
>>>>- }
>>>
>>>I like the fact that it removes the above part.
>>>
>>>>+another_round:
>>>>+ __this_cpu_inc(softnet_data.processed);
>>>>+ dev = skb->dev;
>>>>
>>>> #ifdef CONFIG_NET_CLS_ACT
>>>> if (skb->tc_verd& TC_NCLS) {
>>>>@@ -3153,7 +3153,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
>>>> #endif
>>>>
>>>> list_for_each_entry_rcu(ptype,&ptype_all, list) {
>>>>- if (!ptype->dev || ptype->dev == skb->dev) {
>>>>+ if (!ptype->dev || ptype->dev == dev) {
>>>> if (pt_prev)
>>>> ret = deliver_skb(skb, pt_prev, orig_dev);
>>>> pt_prev = ptype;
>>>
>>>Inside the loop, we should only do exact match delivery, for
>>>&ptype_all and for&ptype_base[ntohs(type)& PTYPE_HASH_MASK]:
>>>
>>> list_for_each_entry_rcu(ptype,&ptype_all, list) {
>>>- if (!ptype->dev || ptype->dev == dev) {
>>>+ if (ptype->dev == dev) {
>>> if (pt_prev)
>>> ret = deliver_skb(skb, pt_prev, orig_dev);
>>> pt_prev = ptype;
>>> }
>>> }
>>>
>>>
>>> list_for_each_entry_rcu(ptype,
>>> &ptype_base[ntohs(type)& PTYPE_HASH_MASK], list) {
>>> if (ptype->type == type&&
>>>- (ptype->dev == null_or_dev || ptype->dev == skb->dev)) {
>>>+ (ptype->dev == skb->dev)) {
>>> if (pt_prev)
>>> ret = deliver_skb(skb, pt_prev, orig_dev);
>>> pt_prev = ptype;
>>> }
>>> }
>>>
>>>After leaving the loop, we can do wilcard delivery, if skb is not NULL.
>>>
>>> list_for_each_entry_rcu(ptype,&ptype_all, list) {
>>>- if (!ptype->dev || ptype->dev == dev) {
>>>+ if (!ptype->dev) {
>>> if (pt_prev)
>>> ret = deliver_skb(skb, pt_prev, orig_dev);
>>> pt_prev = ptype;
>>> }
>>> }
>>>
>>>
>>> list_for_each_entry_rcu(ptype,
>>> &ptype_base[ntohs(type)& PTYPE_HASH_MASK], list) {
>>>- if (ptype->type == type&&
>>>- (ptype->dev == null_or_dev || ptype->dev == skb->dev)) {
>>>+ if (ptype->type == type&& !ptype->dev) {
>>> if (pt_prev)
>>> ret = deliver_skb(skb, pt_prev, orig_dev);
>>> pt_prev = ptype;
>>> }
>>> }
>>>
>>>This would reduce the number of tests inside the
>>>list_for_each_entry_rcu() loops. And because we match only ptype->dev
>>>== dev inside the loop and !ptype->dev outside the loop, this should
>>>avoid duplicate delivery.
>>
>>Would you care to put this into patch so I can see the whole picture?
>>Thanks.
>
>Here is what I have in mind. It is based on your previous DRAFT patch, and don't modify rx_handlers yet.
>
>Only compile tested !!
>
>I don't know if every pieces are at the right place. I wonder what to
>do with CONFIG_NET_CLS_ACT part, that currently is between ptype_all
>and ptype_base processing.
>
>Anyway, the general idea is there.
>
> Nicolas.
>
> net/core/dev.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 files changed, 60 insertions(+), 10 deletions(-)
>
>diff --git a/net/core/dev.c b/net/core/dev.c
>index e5dba47..7e007a9 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -3117,7 +3117,6 @@ static int __netif_receive_skb(struct sk_buff *skb)
> rx_handler_func_t *rx_handler;
> struct net_device *dev;
> struct net_device *orig_dev;
>- struct net_device *null_or_dev;
> int ret = NET_RX_DROP;
> __be16 type;
>
>@@ -3130,9 +3129,6 @@ static int __netif_receive_skb(struct sk_buff *skb)
> if (netpoll_receive_skb(skb))
> return NET_RX_DROP;
>
>- skb->skb_iif = skb->dev->ifindex;
>- orig_dev = skb->dev;
>-
> skb_reset_network_header(skb);
> skb_reset_transport_header(skb);
> skb->mac_len = skb->network_header - skb->mac_header;
>@@ -3143,6 +3139,8 @@ static int __netif_receive_skb(struct sk_buff *skb)
>
> another_round:
> __this_cpu_inc(softnet_data.processed);
>+ skb->skb_iif = skb->dev->ifindex;
>+ orig_dev = skb->dev;
orig_dev should be set at the end of the loop. Now you are going to have
it always the same as dev and skb->dev.
> dev = skb->dev;
>
> #ifdef CONFIG_NET_CLS_ACT
>@@ -3152,8 +3150,13 @@ another_round:
> }
> #endif
>
>+ /*
>+ * Deliver to ptype_all protocol handlers that match current dev.
>+ * This happens before rx_handler is given a chance to change skb->dev.
>+ */
>+
> list_for_each_entry_rcu(ptype, &ptype_all, list) {
>- if (!ptype->dev || ptype->dev == dev) {
>+ if (ptype->dev == dev) {
> if (pt_prev)
> ret = deliver_skb(skb, pt_prev, orig_dev);
> pt_prev = ptype;
>@@ -3167,6 +3170,31 @@ another_round:
> ncls:
> #endif
>
>+ /*
>+ * Deliver to ptype_base protocol handlers that match current dev.
>+ * This happens before rx_handler is given a chance to change skb->dev.
>+ */
>+
>+ type = skb->protocol;
>+ list_for_each_entry_rcu(ptype,
>+ &ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
>+ if (ptype->type == type && ptype->dev == skb->dev) {
>+ if (pt_prev)
>+ ret = deliver_skb(skb, pt_prev, orig_dev);
>+ pt_prev = ptype;
>+ }
>+ }
I'm not sure it is ok to deliver ptype_base here. See comment above
ptype_head() (I'm not sure I understand that correctly)
>+
>+ /*
>+ * Call rx_handler for current device.
>+ * If rx_handler return NULL, skip wilcard protocol handler delivery.
>+ * Else, if skb->dev changed, restart the whole delivery process, to
>+ * allow for device nesting.
>+ *
>+ * Warning:
>+ * rx_handlers must kfree_skb(skb) if they return NULL.
Well this is not true. They can return NULL and call netif_rx as they
have before. No changes necessary I believe.
>+ */
>+
> rx_handler = rcu_dereference(dev->rx_handler);
> if (rx_handler) {
> if (pt_prev) {
>@@ -3176,10 +3204,15 @@ ncls:
> skb = rx_handler(skb);
> if (!skb)
> goto out;
>- if (dev != skb->dev)
>+ if (skb->dev != dev)
> goto another_round;
> }
>
>+ /*
>+ * FIXME: The part below should use rx_handler instead of being hard
>+ * coded here.
I'm not sure it is doable atm. For bridge and bond it should not be a
problem, but for macvlan, there is possible to have macvlans and vlans
on the same dev. This possibility should persist.
/me scratches head on the idea to have multiple rx_handlers although it
was his original idea....
>+ */
>+
> if (vlan_tx_tag_present(skb)) {
> if (pt_prev) {
> ret = deliver_skb(skb, pt_prev, orig_dev);
>@@ -3192,16 +3225,33 @@ ncls:
> goto out;
> }
>
>+ /*
>+ * FIXME: Can't this be moved into the rx_handler for bonding,
>+ * or into a futur rx_handler for vlan?
This hook is something I do not like at all :/ But anyway if should be in vlan
part I think.
>+ */
>+
> vlan_on_bond_hook(skb);
>
>- /* deliver only exact match when indicated */
>- null_or_dev = skb->deliver_no_wcard ? skb->dev : NULL;
>+ /*
>+ * Deliver to wildcard ptype_all protocol handlers.
>+ */
>+
>+ list_for_each_entry_rcu(ptype, &ptype_all, list) {
>+ if (!ptype->dev) {
>+ if (pt_prev)
>+ ret = deliver_skb(skb, pt_prev, orig_dev);
>+ pt_prev = ptype;
>+ }
>+ }
>+
>+ /*
>+ * Deliver to wildcard ptype_all protocol handlers.
>+ */
>
> type = skb->protocol;
> list_for_each_entry_rcu(ptype,
> &ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
>- if (ptype->type == type &&
>- (ptype->dev == null_or_dev || ptype->dev == skb->dev)) {
>+ if (ptype->type == type && !ptype->dev) {
> if (pt_prev)
> ret = deliver_skb(skb, pt_prev, orig_dev);
> pt_prev = ptype;
>--
>1.7.2.3
>
>
>
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