netdev - RE: [RFC net-next (v2) 11/14] igb: set maximal number of default RSS queues

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Date:	Mon, 25 Jun 2012 17:31:30 +0000
From:	"Vick, Matthew" <matthew.vick@...el.com>
To:	Yuval Mintz <yuvalmin@...adcom.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"eilong@...adcom.com" <eilong@...adcom.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
Subject: RE: [RFC net-next (v2) 11/14] igb: set maximal number of default
 RSS queues

> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of Yuval Mintz
> Sent: Monday, June 25, 2012 4:46 AM
> To: davem@...emloft.net; netdev@...r.kernel.org
> Cc: eilong@...adcom.com; Yuval Mintz; Kirsher, Jeffrey T
> Subject: [RFC net-next (v2) 11/14] igb: set maximal number of default
> RSS queues
> 
> Signed-off-by: Yuval Mintz <yuvalmin@...adcom.com>
> Signed-off-by: Eilon Greenstein <eilong@...adcom.com>
> 
> Cc: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
> b/drivers/net/ethernet/intel/igb/igb_main.c
> index 01ced68..b11ee60 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -2465,7 +2465,8 @@ static int __devinit igb_sw_init(struct
> igb_adapter *adapter)
>  		break;
>  	}
> 
> -	adapter->rss_queues = min_t(u32, max_rss_queues,
> num_online_cpus());
> +	adapter->rss_queues = min_t(u32, max_rss_queues,
> +				    netif_get_num_default_rss_queues());
> 
>  	/* Determine if we need to pair queues. */
>  	switch (hw->mac.type) {
> --
> 1.7.9.rc2

Since igb supports a maximum of 8 RSS queues anyway, it's generally unaffected by this change. That being said, I'm confused about what you're trying to accomplish--is it to standardize the number of RSS queues or limit the number of interrupts by default? Or is it the former with a hope that it will trickle down to the latter?

For example, if you take an igb device that supports 8 RSS queues (say, I350) and you change the default to 4 RSS queues, you will end up with the same number of interrupt vectors being requested as we will disable queue pairing and request separate vectors for Rx/Tx queues. I haven't looked at the other drivers affected by this RFC, but it's possible other drivers behave the same way.

Matthew

Matthew Vick
Linux Development
LAN Access Division
Intel Corporation


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