netdev - RE: [RFC 1/2] net/ethtool: Add new coalescing parameter for queue

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Date:	Tue, 8 Dec 2015 19:40:43 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Florian Fainelli <f.fainelli@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"bwh@...nel.org" <bwh@...nel.org>
CC:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"alexander.duyck@...il.com" <alexander.duyck@...il.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Nelson, Shannon" <shannon.nelson@...el.com>,
	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	"Williams, Mitch A" <mitch.a.williams@...el.com>,
	"ogerlitz@...lanox.com" <ogerlitz@...lanox.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"jiri@...lanox.com" <jiri@...lanox.com>,
	"sfeldma@...il.com" <sfeldma@...il.com>,
	"gospo@...ulusnetworks.com" <gospo@...ulusnetworks.com>,
	"sasha.levin@...cle.com" <sasha.levin@...cle.com>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"tj@...nel.org" <tj@...nel.org>,
	"cascardo@...hat.com" <cascardo@...hat.com>,
	"corbet@....net" <corbet@....net>
Subject: RE: [RFC 1/2] net/ethtool: Add new coalescing parameter for queue



> On 07/12/15 20:42, kan.liang@...el.com wrote:
> > From: Kan Liang <kan.liang@...el.com>
> >
> > Intrdouce "queue" option for coalesce getting and setting.
> > For coalesce getting, only the coalescing parameters from specific
> > queue will be passed to user space.
> > For coalesce setting, the coalescing parameters will only be applied
> > to specific queue.
> > If the queue is set to -1, the coalescing parameters will apply to all
> > queues.
> 
> This looks like a good start, but there are a few things that need to be
> clarified, in particular:
> 
> - if the number of TX and RX queues differ, but the ethtool coalesce
> structure contains parameters that affect both the RX and TX side, and the
> queue number is invalid/non-existent for one of these sides, what is the
> expected outcome? Same question with specifying a queue number, with
> RX queue N not belonging to the same queue pair as TX queue N?
>
I thing I should introduce "tx_queue" and "rx_queue" separately
in next version.
 
> - from an user perspective do we want to iterate over all queues to set
> their parameters, or should we have a queue bitmask parameter which
> allows setting them with the same settings in one shot? What would be
> the appropriate bitmask size then (32-bits with 16-bits for TX and 16-bits
> for RX might be too small)?
> 

It's a good idea to use queue bitmask, however I have no idea how many
Bits should we reserve for TX and RX queues.
For my test platform, there are 48 queue pair. So 48 bits are needed for TX
and another 48 bits for RX.
There could be more queues in other plarforms...

Thanks,
Kan