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Date: Thu, 2 Jan 2014 13:07:04 +0800
From: Zhi Yong Wu <zwu.kernel@...il.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Tom Herbert <therbert@...gle.com>,
Linux Netdev List <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] tun: Add support for RFS on tun flows
On Thu, Jan 2, 2014 at 12:44 PM, Jason Wang <jasowang@...hat.com> wrote:
> On 12/22/2013 06:54 PM, Zhi Yong Wu wrote:
>> From: Tom Herbert <therbert@...gle.com>
>>
>> This patch adds support so that the rps_flow_tables (RFS) can be
>> programmed using the tun flows which are already set up to track flows
>> for the purposes of queue selection.
>>
>> On the receive path (corresponding to select_queue and tun_net_xmit) the
>> rxhash is saved in the flow_entry. The original code only does flow
>> lookup in select_queue, so this patch adds a flow lookup in tun_net_xmit
>> if num_queues == 1 (select_queue is not called from
>> dev_queue_xmit->netdev_pick_tx in that case).
>>
>> The flow is recorded (processing CPU) in tun_flow_update (TX path), and
>> reset when flow is deleted.
>>
>> Signed-off-by: Tom Herbert <therbert@...gle.com>
>> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>> ---
>> drivers/net/tun.c | 37 +++++++++++++++++++++++++++++++++++--
>> 1 files changed, 35 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index a17a701..3cf0457 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -152,6 +152,7 @@ struct tun_flow_entry {
>> struct tun_struct *tun;
>>
>> u32 rxhash;
>> + u32 rps_rxhash;
>> int queue_index;
>> unsigned long updated;
>> };
>> @@ -220,6 +221,7 @@ static struct tun_flow_entry *tun_flow_create(struct tun_struct *tun,
>> rxhash, queue_index);
>> e->updated = jiffies;
>> e->rxhash = rxhash;
>> + e->rps_rxhash = 0;
>> e->queue_index = queue_index;
>> e->tun = tun;
>> hlist_add_head_rcu(&e->hash_link, head);
>> @@ -232,6 +234,7 @@ static void tun_flow_delete(struct tun_struct *tun, struct tun_flow_entry *e)
>> {
>> tun_debug(KERN_INFO, tun, "delete flow: hash %u index %u\n",
>> e->rxhash, e->queue_index);
>> + sock_rps_reset_flow_hash(e->rps_rxhash);
>> hlist_del_rcu(&e->hash_link);
>> kfree_rcu(e, rcu);
>> --tun->flow_count;
>> @@ -325,6 +328,7 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
>> /* TODO: keep queueing to old queue until it's empty? */
>> e->queue_index = queue_index;
>> e->updated = jiffies;
>> + sock_rps_record_flow_hash(e->rps_rxhash);
>> } else {
>> spin_lock_bh(&tun->lock);
>> if (!tun_flow_find(head, rxhash) &&
>> @@ -341,6 +345,18 @@ unlock:
>> rcu_read_unlock();
>> }
>>
>> +/**
>> + * Save the hash received in the stack receive path and update the
>> + * flow_hash table accordingly.
>> + */
>> +static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
>> +{
>> + if (unlikely(e->rps_rxhash != hash)) {
>> + sock_rps_reset_flow_hash(e->rps_rxhash);
>> + e->rps_rxhash = hash;
>> + }
>> +}
>> +
>> /* We try to identify a flow through its rxhash first. The reason that
>> * we do not check rxq no. is because some cards(e.g 82599), chooses
>> * the rxq based on the txq where the last packet of the flow comes. As
>> @@ -361,9 +377,10 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb)
>> txq = skb_get_hash(skb);
>> if (txq) {
>> e = tun_flow_find(&tun->flows[tun_hashfn(txq)], txq);
>> - if (e)
>> + if (e) {
>> txq = e->queue_index;
>> - else
>> + tun_flow_save_rps_rxhash(e, txq);
>> + } else
>
> This looks wrong, txq is the queue index here. We should do this before
> txq = e->queue_index.
Good catch, will try to post one patch to fix it after the perf tests
are done, thanks.
>
> Did you test the patch? You can simply verify the basic function by
No so far, be planning to do its perf tests, do you have any good suggestions?
> checking whether the rx softirq were done in the same cpu where vhost is
> running.
>> /* use multiply and shift instead of expensive divide */
>> txq = ((u64)txq * numqueues) >> 32;
>> } else if (likely(skb_rx_queue_recorded(skb))) {
>> @@ -728,6 +745,22 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>> if (txq >= tun->numqueues)
>> goto drop;
>>
>> + if (tun->numqueues == 1) {
>> + /* Select queue was not called for the skbuff, so we extract the
>> + * RPS hash and save it into the flow_table here.
>> + */
>> + __u32 rxhash;
>> +
>> + rxhash = skb_get_hash(skb);
>> + if (rxhash) {
>> + struct tun_flow_entry *e;
>> + e = tun_flow_find(&tun->flows[tun_hashfn(rxhash)],
>> + rxhash);
>> + if (e)
>> + tun_flow_save_rps_rxhash(e, rxhash);
>> + }
>> + }
>> +
>> tun_debug(KERN_INFO, tun, "tun_net_xmit %d\n", skb->len);
>>
>> BUG_ON(!tfile);
>
--
Regards,
Zhi Yong Wu
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