netdev - Re: Setting RPS affinities from network driver

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Date:	Thu, 19 Feb 2015 21:07:21 -0500
From:	Jonathon Reinhart <jonathon.reinhart@...il.com>
To:	Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: Setting RPS affinities from network driver

I don't know if this is a good idea. It seems like allowing the driver to
set this default configuration opens the door to a whole slew of driver-
specific config customizations.

As as user, I wouldn't expect one driver to have a different default
value of rps_cpus than another driver. Furthermore, I could imagine a
case where a user expects rps_cpus to default to zero for all of his
NICs, and has other CPU affinity settings applied (think realtime).

In my opinion, this should be left to userspace. It's not that hard to
add it to your init scripts.


On Wed, Feb 18, 2015 at 10:47 AM, Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> Thanks Tom,
>
> Will try to implement something like a library function which can be used
> by any driver.
>
> Regards,
> Sunil.
>
> On Wed, Feb 18, 2015 at 9:14 PM, Tom Herbert <therbert@...gle.com> wrote:
>> On Tue, Feb 17, 2015 at 10:16 PM, Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
>>> Hi,
>>>
>>> I am writing a network driver for a multicore SOC with a on-board
>>> network interface and would like to set RPS affinities from driver by
>>> default. So that the network performance is good with whatever driver
>>> supplied. Ofcourse these can be further adjusted from userspace
>>> anyways.
>>>
>>> Is there a way to set RPS settings from driver itself ?
>>> The only issue i am seeing is while setting 'rps_needed' key.
>>>
>> There is nothing to prevent this, but it would be really cool to make
>> this into a library function that drivers can call to initialize RPS
>> in some sane way (you might want to look at cpu_rmap).
>>
>>> static_key_slow_inc(&rps_needed);
>>>
>>> Currently this is not exported, so having issues while compiling
>>> driver as module.
>>>
>>> If i export this symbol, will it be acceptable ?
>>>
>> Seems okay to me.
>>
>> Thanks,
>> Tom
>>
>>>
>>> Thanks,
>>> Sunil.
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