linux-kernel - Re: [RFC 0/7] Add support to process rx packets in thread

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Message-ID: <80490faa-f9e8-3bac-a645-7458b9d6aa62@gmail.com>
Date:   Fri, 24 Jul 2020 15:28:03 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Rakesh Pillai <pillair@...eaurora.org>,
        'Andrew Lunn' <andrew@...n.ch>
Cc:     ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvalo@...eaurora.org,
        johannes@...solutions.net, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, dianders@...omium.org, evgreen@...omium.org
Subject: Re: [RFC 0/7] Add support to process rx packets in thread

On 7/23/20 11:20 PM, Rakesh Pillai wrote:
> 
> 
>> -----Original Message-----
>> From: Florian Fainelli <f.fainelli@...il.com>
>> Sent: Friday, July 24, 2020 12:33 AM
>> To: Rakesh Pillai <pillair@...eaurora.org>; 'Andrew Lunn'
>> <andrew@...n.ch>
>> Cc: ath10k@...ts.infradead.org; linux-wireless@...r.kernel.org; linux-
>> kernel@...r.kernel.org; kvalo@...eaurora.org; johannes@...solutions.net;
>> davem@...emloft.net; kuba@...nel.org; netdev@...r.kernel.org;
>> dianders@...omium.org; evgreen@...omium.org
>> Subject: Re: [RFC 0/7] Add support to process rx packets in thread
>>
>> On 7/23/20 11:21 AM, Rakesh Pillai wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Florian Fainelli <f.fainelli@...il.com>
>>>> Sent: Tuesday, July 21, 2020 11:35 PM
>>>> To: Andrew Lunn <andrew@...n.ch>; Rakesh Pillai
>> <pillair@...eaurora.org>
>>>> Cc: ath10k@...ts.infradead.org; linux-wireless@...r.kernel.org; linux-
>>>> kernel@...r.kernel.org; kvalo@...eaurora.org;
>> johannes@...solutions.net;
>>>> davem@...emloft.net; kuba@...nel.org; netdev@...r.kernel.org;
>>>> dianders@...omium.org; evgreen@...omium.org
>>>> Subject: Re: [RFC 0/7] Add support to process rx packets in thread
>>>>
>>>> On 7/21/20 10:25 AM, Andrew Lunn wrote:
>>>>> On Tue, Jul 21, 2020 at 10:44:19PM +0530, Rakesh Pillai wrote:
>>>>>> NAPI gets scheduled on the CPU core which got the
>>>>>> interrupt. The linux scheduler cannot move it to a
>>>>>> different core, even if the CPU on which NAPI is running
>>>>>> is heavily loaded. This can lead to degraded wifi
>>>>>> performance when running traffic at peak data rates.
>>>>>>
>>>>>> A thread on the other hand can be moved to different
>>>>>> CPU cores, if the one on which its running is heavily
>>>>>> loaded. During high incoming data traffic, this gives
>>>>>> better performance, since the thread can be moved to a
>>>>>> less loaded or sometimes even a more powerful CPU core
>>>>>> to account for the required CPU performance in order
>>>>>> to process the incoming packets.
>>>>>>
>>>>>> This patch series adds the support to use a high priority
>>>>>> thread to process the incoming packets, as opposed to
>>>>>> everything being done in NAPI context.
>>>>>
>>>>> I don't see why this problem is limited to the ath10k driver. I expect
>>>>> it applies to all drivers using NAPI. So shouldn't you be solving this
>>>>> in the NAPI core? Allow a driver to request the NAPI core uses a
>>>>> thread?
>>>>
>>>> What's more, you should be able to configure interrupt affinity to steer
>>>> RX processing onto a desired CPU core, is not that working for you
>>>> somehow?
>>>
>>> Hi Florian,
>>> Yes, the affinity of IRQ does work for me.
>>> But the affinity of IRQ does not happen runtime based on load.
>>
>> It can if you also run irqbalance.
> 
> 
> Hi Florian,
> 
> Is it some kernel feature ?  Sorry I am not aware of this ?
> I know it can be done in userspace.

The kernel interface is /proc/<irq>/smp_affinity and the users-space
implementation resides here:

https://github.com/Irqbalance/irqbalance
-- 
Florian