Re: [RFC PATCH v2 10/10] ixgbe: Add support for set_channels ethtool operation

From: Alexander Duyck <alexander.h.duyck@intel.com>
To: Ben Hutchings <bhutchings@solarflare.com>
Cc: "Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@intel.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"therbert@google.com" <therbert@google.com>,
	"ycai@google.com" <ycai@google.com>,
	"eric.dumazet@gmail.com" <eric.dumazet@gmail.com>,
	"davem@davemloft.net" <davem@davemloft.net>
Subject: Re: [RFC PATCH v2 10/10] ixgbe: Add support for set_channels ethtool operation
Date: Wed, 23 Jan 2013 14:31:49 -0800	[thread overview]
Message-ID: <510064D5.2020905@intel.com> (raw)
In-Reply-To: <1358976045.2658.18.camel@bwh-desktop.uk.solarflarecom.com>

On 01/23/2013 01:20 PM, Ben Hutchings wrote:
> On Wed, 2013-01-16 at 16:30 +0000, Waskiewicz Jr, Peter P wrote:
>> On Wed, 2013-01-16 at 16:19 +0000, Ben Hutchings wrote:
>>> On Thu, 2013-01-10 at 10:58 -0800, Alexander Duyck wrote:
>>>> This change adds support for the ethtool set_channels operation.
>>>>
>>>> Since the ixgbe driver has to support DCB as well as the other modes the
>>>> assumption I made here is that the number of channels in DCB modes refers
>>>> to the number of queues per traffic class, not the number of queues total.
>>>>
>>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>>> In DCB mode are there separate IRQs for the different classes?
>> Yes.  The Rx packet buffer is split into multiple packet buffers, one
>> for each online class.  After that, it's just queues assigned to the
>> packet buffers, and interrupts assigned however you want them to be.
> Right, I think we've been through this before.  And I can see how it
> would be more useful for users to specify number of RX queues per
> priority level.  But that's not what was specified...
>
> I'm afraid the 'channels' ethtool operations have turned into a mess...
> I can't see how to get to a reasonable generic definition of what they
> should do.
>
> Ben.

Actually it looks like most of the drivers (I looked at bnx, bnx2x, tg3,
and qlcnic) are using the set_queues call in a similar way.  What they
end up doing is using the value and plugging it into their TSS/RSS
fields in their private structures.  From what I can tell in
bnx2x_setup_tc they may do exactly the same thing we are currently doing
for DCB since they use the BNX2X_NUM_ETH_QUEUES value that they set in
their set_channels call to set the number of queues they use per traffic
class.  I would say the usage is actually pretty consistent between
bnx2x and ixgbe based on this, even if it isn't exactly correct.

For now I would say all of the drivers are using the set_channels
operation to specify the number of Tx/Rx queues, or queue pairs per
traffic class.  So for non-DCB NICs this means it is setting exactly
that number of queues, and for DCB capable nics it means num_tcs times
the specified number of queues.

Thanks,

Alex