netdev - Re: [RFC PATCH 00/10] Make XPS usable within ixgbe

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Date:	Tue, 03 Jul 2012 15:41:59 -0700
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Tom Herbert <therbert@...gle.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>
CC:	netdev@...r.kernel.org, davem@...emloft.net,
	jeffrey.t.kirsher@...el.com, edumazet@...gle.com,
	bhutchings@...arflare.com, alexander.duyck@...il.com
Subject: Re: [RFC PATCH 00/10] Make XPS usable within ixgbe

On 7/3/2012 3:30 PM, Tom Herbert wrote:
> Hi Alexander,
>
> Thanks for this work!
>
> Some general comments:
>
> 1) skb_tx_hash is called from a handful of drivers (bnx2x, ixgbe,
> mlx4, and bonding).  Would it make sent to call xps_get_cpu from that
> function (unfortunately the use of ndo_select_queue is likely
> bypassing xps unnecessarily in these drivers).

I suspect we can get rid of the select_queue cases for at least
bnx2x, ixgbe, and mlx4. We might need to be a bit clever to resolve
the mlx4 case but should be doable.

Anyways I would like to see these cases refactored away.

> 2) Instead of (or maybe in addition to) allowing driver to program xps
> maps, we could parameterize get_xps_cpu to optionally include a bit
> map of acceptable queues.  This would be useful to define a
> hierarchical queue selection (like first choose a set for QoS, then
> amongst those chose one base on xps).
>

Agreed.

We likely need something like (2) to get this to work with mqprio and
other QOS schemes in use.

.John
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