netdev - Re: [RFC net-next 05/14] Fix intel/ixgbevf

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Date:	Tue, 19 Jun 2012 19:06:53 +0300
From:	"Eilon Greenstein" <eilong@...adcom.com>
To:	"Alexander Duyck" <alexander.h.duyck@...el.com>
cc:	"Yuval Mintz" <yuvalmin@...adcom.com>, netdev@...r.kernel.org,
	davem@...emloft.net, "Jeff Kirsher" <jeffrey.t.kirsher@...el.com>
Subject: Re: [RFC net-next 05/14] Fix intel/ixgbevf

On Tue, 2012-06-19 at 08:39 -0700, Alexander Duyck wrote:
> On 06/19/2012 08:13 AM, Yuval Mintz wrote:
> > 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/ixgbevf/ixgbevf_main.c |    5 +++--
> >  1 files changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
> > index f69ec42..3ad46c2 100644
> > --- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
> > +++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
> > @@ -2014,7 +2014,7 @@ err_tx_ring_allocation:
> >  static int ixgbevf_set_interrupt_capability(struct ixgbevf_adapter *adapter)
> >  {
> >  	int err = 0;
> > -	int vector, v_budget;
> > +	int vector, v_budget, ncpu;
> >  
> >  	/*
> >  	 * It's easy to be greedy for MSI-X vectors, but it really
> > @@ -2022,8 +2022,9 @@ static int ixgbevf_set_interrupt_capability(struct ixgbevf_adapter *adapter)
> >  	 * than CPU's.  So let's be conservative and only ask for
> >  	 * (roughly) twice the number of vectors as there are CPU's.
> >  	 */
> > +	ncpu = min_t(int, num_online_cpus(), DEFAULT_MAX_NUM_RSS_QUEUES);
> >  	v_budget = min(adapter->num_rx_queues + adapter->num_tx_queues,
> > -		       (int)(num_online_cpus() * 2)) + NON_Q_VECTORS;
> > +		       ncpu * 2) + NON_Q_VECTORS;
> >  
> >  	/* A failure in MSI-X entry allocation isn't fatal, but it does
> >  	 * mean we disable MSI-X capabilities of the adapter. */
> This change is pointless on the ixgbevf driver.  The VF hardware can
> support at most 4 RSS queues.  As such num_rx_queues + num_tx_queues
> will never exceed 8 so you are essentially adding a necessary min(x,8).

It is pointless with the current value, but if someone will edit the
kernel source code and replace the 8 with a 2, it will become
meaningful. The compiler will optimize this part, and I think that for
completion, it is best to keep this reference so a future default number
change will not be missed.

Eilon


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