netdev - Re: [PATCH net-next-2.6] rps: allocate rx queues in register

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Date:	Fri, 24 Sep 2010 11:21:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-net-drivers@...arflare.com" <linux-net-drivers@...arflare.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH net-next-2.6] rps: allocate rx queues in
 register_netdevice only

Le vendredi 24 septembre 2010 à 01:15 -0700, John Fastabend a écrit :
> On 9/23/2010 8:26 PM, Eric Dumazet wrote:
> > 
> >> Also, I dont understand why we need to restrict
> >> netif_set_real_num_rx_queues() to lower the count.
> >> This wastes memory.
> >>
> >> Why dont we allocate dev->_rx once we know the real count, not in
> >> alloc_netdev_mq() but in register_netdevice() ?
> >>
> 
> Eric,
> 
> At least in the TX case we may not "know" until later how many
> tx_queues we want to use. For example it could change based on
> enabling/disabling features or available interrupts. So we use
> num_tx_queues as the max we ever expect to use and then
> netif_set_real_num_tx_queues() sets the number we want to use.
> 
> I presume for rx queues there are similar cases where features and
> available interrupts may determine how many rx queues are needed.
> 
> Moving the allocation later could help drivers make better max number
> of queue decisions. But, I think we still need the
> netif_set_num_rx_queues() and netif_set_num_tx_queues(). Although this
> does end up wasting memory as you pointed out.
> 

Note I am not against having netif_set_num_rx_queues() and
netif_set_num_tx_queues(). My patch was a cleanup, not an alternative.


If I take a look at sysfs stuff, on a machine with a bnx2 adapter,
single queue, I get :

/sys/class/net/eth0/queues/rx-0/rps_cpus
/sys/class/net/eth0/queues/rx-0/rps_flow_cnt
/sys/class/net/eth0/queues/rx-1/rps_cpus
/sys/class/net/eth0/queues/rx-1/rps_flow_cnt
/sys/class/net/eth0/queues/rx-2/rps_cpus
/sys/class/net/eth0/queues/rx-2/rps_flow_cnt
/sys/class/net/eth0/queues/rx-3/rps_cpus
/sys/class/net/eth0/queues/rx-3/rps_flow_cnt
/sys/class/net/eth0/queues/rx-4/rps_cpus
/sys/class/net/eth0/queues/rx-4/rps_flow_cnt
/sys/class/net/eth0/queues/rx-5/rps_cpus
/sys/class/net/eth0/queues/rx-5/rps_flow_cnt
/sys/class/net/eth0/queues/rx-6/rps_cpus
/sys/class/net/eth0/queues/rx-6/rps_flow_cnt
/sys/class/net/eth0/queues/rx-7/rps_cpus
/sys/class/net/eth0/queues/rx-7/rps_flow_cnt

Thats a lot of extra memory and administrator confusion.

We all agree :)


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