netdev - RE: netif_receive_skb is taking long time

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Message-ID: <BN6PR02MB2641D817810960AAE59B9CDEB7F70@BN6PR02MB2641.namprd02.prod.outlook.com>
Date:   Thu, 25 Oct 2018 17:22:02 +0000
From:   Keyur Amrutbhai Patel <keyurp@...inx.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: netif_receive_skb is taking long time

Hi Eric,

First of all thank you for replying and giving some spotlight.

First step would be to read Documentation/networking/scaling.txt and see if anything there helps.
 - This is good article. I had gone through it.  Any suggestion on RSS? How to configure it? Do I need to take care anything specially in my NIC driver?

Have you tried to profile the kernel and see if some contention or hot function appears ?
- I have added time stampings in different functions. That is how I came to know that almost ~3375 neno seconds are used by just " netif_receive_skb " don’t know why. With less than that time my DMA operation is finishes and descriptors are managed.
Current time consuming function are " netif_receive_skb " and " napi_alloc_skb " these two function calls are taking maximum about of time

Maybe use a faster cpu, or remove not needed features like too heavy netfilter rules.
- I am using Intex Xeon Platinum series processors. These are fast enough CPUs available in market with 64 cores. 2 CPU nodes (each has 32 core)

We can not really answer your question, you do not provide enough information.
- Please let me know what additional details you need. We have 6 queues in HW. Each is mapped to MSI-X vector. Each vector is giving interrupt on different CPU. From interrupt I am scheduling napi and from napi poll function I am getting DMA page and constructing skb and passing it to network layer with "netif_receive_skb".

Let me know additional details which are required.

Regards,
Keyur

-----Original Message-----
From: Eric Dumazet <eric.dumazet@...il.com> 
Sent: Thursday, October 25, 2018 10:38 PM
To: Keyur Amrutbhai Patel <keyurp@...inx.com>; netdev@...r.kernel.org
Subject: Re: netif_receive_skb is taking long time

EXTERNAL EMAIL

On 10/25/2018 08:39 AM, Keyur Amrutbhai Patel wrote:
> Hi,
>
> In my NIC driver "netif_receive_skb" is taking too long time. Almost 3375 neno seconds. Which is more than whole packet processing from interrupt.
>
> Could anyone please help me to understand what could be the reason behind this? How to solve it to take minimum time?
>
> Is there any standard calls which we need to follow in order to get faster performance?
>

First step would be to read Documentation/networking/scaling.txt and see if anything there helps.

Have you tried to profile the kernel and see if some contention or hot function appears ?

Maybe use a faster cpu, or remove not needed features like too heavy netfilter rules.

We can not really answer your question, you do not provide enough information.