netdev - Re: [net-next PATCH 2/2] drivers: net: cpsw: add separate napi for tx packet handling for performance improvment

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Date:	Thu, 30 Jul 2015 11:42:09 +0530
From:	Mugunthan V N <mugunthanvnm@...com>
To:	Francois Romieu <romieu@...zoreil.com>
CC:	<netdev@...r.kernel.org>, <davem@...emloft.net>
Subject: Re: [net-next PATCH 2/2] drivers: net: cpsw: add separate napi for
 tx packet handling for performance improvment

On Thursday 30 July 2015 04:27 AM, Francois Romieu wrote:
> Mugunthan V N <mugunthanvnm@...com> :
>> On Wednesday 29 July 2015 04:00 AM, Francois Romieu wrote:
>>> Mugunthan V N <mugunthanvnm@...com> :
>>>> On Tuesday 28 July 2015 02:52 AM, Francois Romieu wrote:
> [...]
>>>>> cpsw_ndo_stop calls napi_disable: you can remove netif_running.
>>>>>
>>>>
>>>> This netif_running check is to find which interface is up as the
>>>> interrupt is shared by both the interfaces. When first interface is down
>>>> and second interface is active then napi_schedule for first interface
>>>> will fail and second interface napi needs to be scheduled.
>>>>
>>>> So I don't think netif_running needs to be removed.
>>>
>>> Each interface has its own napi tx (resp. rx) context: I would had expected
>>> two unconditional napi_schedule per tx (resp. rx) shared irq, not one.
>>>
>>> I'll read it again after some sleep.
>>>
>>
>> For each interrupt only one napi will be scheduled, when the first
>> interface is down then only second interface napi is scheduled in both
>> tx and rx irqs.
> 
> Ok, I've had some hints from the "Assumptions" section at
> http://processors.wiki.ti.com/index.php/AM335x_CPSW_%28Ethernet%29_Driver%27s_Guide#Dual_Standalone_EMAC_mode
> 
> Why does the driver create 2 rx napi contexts ? They don't run at the
> same time and the port demux is done in cpsw_dual_emac_src_port_detect.
> The driver would work the same with a single rx (resp. tx) napi context
> for both interfaces.
> 

The wiki you had pointed out is old design done on v3.2 and doesn't have
device tree support also. In mainline Dual EMAC implementation has
changed a lot.

I can think of a way with one napi implementation for each rx and tx,
will submit a separate patch for it.

Regards
Mugunthan V N
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