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Date:   Tue, 26 Jun 2018 17:36:30 -0700
From:   "Nambiar, Amritha" <amritha.nambiar@...el.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Tom Herbert <tom@...bertland.com>
Subject: Re: [net-next PATCH v4 5/7] net: Enable Tx queue selection based on
 Rx queues

On 6/26/2018 4:04 AM, Willem de Bruijn wrote:
> On Mon, Jun 25, 2018 at 7:06 PM Amritha Nambiar
> <amritha.nambiar@...el.com> wrote:
>>
>> This patch adds support to pick Tx queue based on the Rx queue(s) map
>> configuration set by the admin through the sysfs attribute
>> for each Tx queue. If the user configuration for receive queue(s) map
>> does not apply, then the Tx queue selection falls back to CPU(s) map
>> based selection and finally to hashing.
>>
>> Signed-off-by: Amritha Nambiar <amritha.nambiar@...el.com>
>> ---
> 
>> +static int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
>>  {
>>  #ifdef CONFIG_XPS
>>         struct xps_dev_maps *dev_maps;
>> -       struct xps_map *map;
>> +       struct sock *sk = skb->sk;
>>         int queue_index = -1;
>>
>>         if (!static_key_false(&xps_needed))
>>                 return -1;
>>
>>         rcu_read_lock();
>> -       dev_maps = rcu_dereference(dev->xps_cpus_map);
>> +       if (!static_key_false(&xps_rxqs_needed))
>> +               goto get_cpus_map;
>> +
>> +       dev_maps = rcu_dereference(dev->xps_rxqs_map);
>>         if (dev_maps) {
>> -               unsigned int tci = skb->sender_cpu - 1;
>> +               int tci = sk_rx_queue_get(sk);
> 
> What if the rx device differs from the tx device?
> 
I think I have 3 options here:
1. Cache the ifindex in sock_common which will introduce a new
additional field in sock_common.
2. Use dev_get_by_napi_id to get the device id. This could be expensive,
if the rxqs_map is set, this will be done on every packet and involves
walking through the hashlist for napi_id lookup.
3. Remove validating device id, similar to how it is in skb_tx_hash
where rx_queue recorded is used and if not, fall through to flow hash
calculation.
What do you think is suitable here?

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