netdev - Re: [net-next 13/13] ixgbe: use per NUMA node lock for FCoE DDP

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Message-Id: <1308009777.31900.87.camel@vi2.jf.intel.com>
Date:	Mon, 13 Jun 2011 17:02:57 -0700
From:	Vasu Dev <vasu.dev@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net,
	Vasu Dev <vasu.dev@...el.com>, netdev@...r.kernel.org,
	gospo@...hat.com
Subject: Re: [net-next 13/13] ixgbe: use per NUMA node lock for FCoE DDP

On Sat, 2011-06-11 at 07:18 +0200, Eric Dumazet wrote:
> > +static void ixgbe_fcoe_lock_init(struct ixgbe_fcoe *fcoe)
> > +{
> > +     int node;
> > +     spinlock_t *node_lock;
> > +
> > +     fcoe->node_lock = kzalloc(sizeof(node_lock) *
> num_possible_nodes(),
> > +                               GFP_KERNEL);
> 
> Hmm...
> 
> 1) Think of what happens if some machine has 3 possible nodes : 0, 2,
> 3
> 
>         -> You should use nr_node_ids instead of num_possible_nodes() 
> 

Just curious won't these both return same values ? Anycase use of
nr_nodes_ids looks better as it is already set. 

> 2) Make sure this block cant have false sharing : Allocate at least a
> full cache line : On a typical 2 node machine, you currently allocate
> 16bytes of memory, and this small block could share a contended cache
> line.

Yeap good point. Thanks

> 
> 
> > +     if (!fcoe->node_lock)

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