Re: [RFC PATCH] fib_hash: improve route deletion scaling on interface drop with lots of interfaces

[David Miller <davem@davemloft.net>]

From: Benjamin LaHaise <bcrl@lhnet.ca>
Date: Mon, 26 Oct 2009 20:03:02 -0400

> Below is a patch to improve the scaling of interface destruction in 
> fib_hash.  The general idea is to tie the fib_alias structure into a 
> list off of net_device and walk that list during a fib_flush() caused 
> by an interface drop.  This makes the resulting flush only have to walk 
> the number of routes attached to an interface rather than the number of 
> routes attached to all interfaces at the expense of a couple of additional 
> pointers in struct fib_alias.
> 
> This patch is against Linus' tree.  I'll post against net-next after a 
> bit more testing and feedback.  With 20,000 interfaces & routes, interface 
> deletion time improves from 53s to 40s.  Note that this is with other changes 
> applied to improve sysfs and procfs scaling, as otherwise those are the 
> bottleneck.  Next up in the network code is rt_cache_flush().  Comments?

On a real router adding and removing routes is happening a lot
whereas interface changes are rare.  You're making a more common
operation more expensive for the sake of a less common one.

> @@ -128,18 +128,19 @@ void fib_select_default(struct net *net,
>  		tb->tb_select_default(tb, flp, res);
>  }
>  
> -static void fib_flush(struct net *net)
> +static void fib_flush(struct net_device *dev)
>  {
>  	int flushed = 0;
>  	struct fib_table *tb;
>  	struct hlist_node *node;
>  	struct hlist_head *head;
>  	unsigned int h;
> +	struct net *net = dev_net(dev);
>  

Please put local variable lines that are longer at the beginning of
the list of variable declarations at the top of a function, not the
other way around which stands out like a sore thumb and looks ugly.