netdev - Re: [PATCH net-2.6] Re: rib_trie / Fix inflate_threshold

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Date:	Mon, 6 Jul 2009 00:23:01 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Paweł Staszewski <pstaszewski@...are.pl>,
	Linux Network Development list <netdev@...r.kernel.org>,
	Robert Olsson <robert@...ur.slu.se>
Subject: Re: [PATCH net-2.6] Re: rib_trie / Fix inflate_threshold_root.
	Now=15 size=11 bits

On Sun, Jul 05, 2009 at 02:32:32PM -0700, Paul E. McKenney wrote:
> On Sun, Jul 05, 2009 at 07:32:08PM +0200, Jarek Poplawski wrote:
> > On Sun, Jul 05, 2009 at 06:20:03PM +0200, Jarek Poplawski wrote:
> > > On Sun, Jul 05, 2009 at 02:30:03AM +0200, Paweł Staszewski wrote:
> > > > Oh
> > > >
> > > > I forgot - please Jarek give me patch with sync rcu and i will make test  
> > > > on preempt kernel
> > > 
> > > Probably non-preempt kernel might need something like this more, but
> > > comparing is always interesting. This patch is based on Paul's
> > > suggestion (I hope).
> > 
> > Hold on ;-) Here is something even better... Syncing after 128 pages
> > might be still too slow, so here is a higher initial value, 1000, plus
> > you can change this while testing in:
> > 
> > /sys/module/fib_trie/parameters/sync_pages
> > 
> > It would be interesting to find the lowest acceptable value.
> 
> Looks like a promising approach to me!
> 
> 							Thanx, Paul

Hmm... As a matter of fact, I'm a bit sceptical now: I'm worrying this
synchronize_rcu done at the lowest acceptable rate could be actually
mostly idle or on the contrary too late. Probably some more complex
(per cpu?) accounting would be necessary to really matter here, but
on the other hand these problems weren't reported often enough.

Thanks,
Jarek P.

> > ---> (synchronize take 8; apply on top of the 2.6.29.x with the last
> >  	all-in-one patch, or net-2.6)
> > 
> >  net/ipv4/fib_trie.c |   12 ++++++++++++
> >  1 files changed, 12 insertions(+), 0 deletions(-)
> > 
> > diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> > index 00a54b2..decc8d0 100644
> > --- a/net/ipv4/fib_trie.c
> > +++ b/net/ipv4/fib_trie.c
> > @@ -71,6 +71,7 @@
> >  #include <linux/netlink.h>
> >  #include <linux/init.h>
> >  #include <linux/list.h>
> > +#include <linux/moduleparam.h>
> >  #include <net/net_namespace.h>
> >  #include <net/ip.h>
> >  #include <net/protocol.h>
> > @@ -164,6 +165,10 @@ static struct tnode *inflate(struct trie *t, struct tnode *tn);
> >  static struct tnode *halve(struct trie *t, struct tnode *tn);
> >  /* tnodes to free after resize(); protected by RTNL */
> >  static struct tnode *tnode_free_head;
> > +static size_t tnode_free_size;
> > +
> > +static int sync_pages __read_mostly = 1000;
> > +module_param(sync_pages, int, 0640);
> > 
> >  static struct kmem_cache *fn_alias_kmem __read_mostly;
> >  static struct kmem_cache *trie_leaf_kmem __read_mostly;
> > @@ -393,6 +398,8 @@ static void tnode_free_safe(struct tnode *tn)
> >  	BUG_ON(IS_LEAF(tn));
> >  	tn->tnode_free = tnode_free_head;
> >  	tnode_free_head = tn;
> > +	tnode_free_size += sizeof(struct tnode) +
> > +			   (sizeof(struct node *) << tn->bits);
> >  }
> > 
> >  static void tnode_free_flush(void)
> > @@ -404,6 +411,11 @@ static void tnode_free_flush(void)
> >  		tn->tnode_free = NULL;
> >  		tnode_free(tn);
> >  	}
> > +
> > +	if (tnode_free_size >= PAGE_SIZE * sync_pages) {
> > +		tnode_free_size = 0;
> > +		synchronize_rcu();
> > +	}
> >  }
> > 
> >  static struct leaf *leaf_new(void)
> > --
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