netdev - Re: [PATCH net-next 1/6] net: skbuff: don't use union for napi_id and sender

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Date:	Fri, 1 Apr 2016 12:49:31 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/6] net: skbuff: don't use union for napi_id and
 sender_cpu



On 04/01/2016 10:55 AM, Eric Dumazet wrote:
> On Fri, 2016-04-01 at 10:13 +0800, Jason Wang wrote:
>
>
>> The problem is we want to support busy polling for tun. This needs
>> napi_id to be passed to tun socket by sk_mark_napi_id() during
>> tun_net_xmit(). But before reaching this, XPS will set sender_cpu will
>> make us can't see correct napi_id.
>>
> Looks like napi_id should have precedence then ?

But then when busy polling is enabled, we may still hit the issue before
commit 2bd82484bb4c5db1d5dc983ac7c409b2782e0154? So looks like sometimes
(e.g for tun), we need both two fields.

>
> Only forwarding should allow the field to be cleared to allow XPS to do
> its job.
>
> Maybe skb_sender_cpu_clear() was removed too early (commit
> 64d4e3431e686dc37ce388ba531c4c4e866fb141)

Not sure I get you, but this will clear napi_id too.

> Look, it is 8pm here, I am pretty sure a solution can be found,
> but I am also need to take a break, I started at 3am today...
>
>
>