netdev - Re: [PATCH net-next 1/2 v2] net sched actions: dump more than TCA_ACT_MAX

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Date:   Tue, 18 Apr 2017 22:32:33 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, jiri@...nulli.us,
        xiyou.wangcong@...il.com
Subject: Re: [PATCH net-next 1/2 v2] net sched actions: dump more than
 TCA_ACT_MAX_PRIO actions per batch

On 17-04-18 09:49 PM, Eric Dumazet wrote:
> On Tue, 2017-04-18 at 21:14 -0400, Jamal Hadi Salim wrote:
>> From: Jamal Hadi Salim <jhs@...atatu.com>
>
> So there is no more limit ? How user is supposed to size the buffer for
> recvmsg() ?
>

That part doesnt change.  Ok, I believe more clarity is needed:->

Current code allows only 32 actions to be dumped at a time.
This code:

So lets i have 128 actions. I can fit them into 10K.
I do recvmsg(..., 32K). This will make about 32K space for me to fill
up the 128 actions. But the code only allows me to send 32
TCA_ACT_MAX_PRIO which takes about 2-3K.
So I will do 4 runs from kernel->user to get 128 actions ;->
User space in tc is trained to expect no more than
TCA_ACT_MAX_PRIO in every batch.

With this change I ask the kernel to fit as many actions as
possible in the 32K (all these 128 will fit in one batch).
Then it has to tell user space how many are in that batch
using TCAA_ACT_COUNT attribute.

Make sense?

cheers,
jamal