netdev - Re: [net-next PATCH V2 5/9] net: frag, per CPU resource, mem limit and LRU list accounting

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Date:	Thu, 29 Nov 2012 09:06:16 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Thomas Graf <tgraf@...g.ch>, Cong Wang <amwang@...hat.com>,
	Patrick McHardy <kaber@...sh.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: [net-next PATCH V2 5/9] net: frag, per CPU resource, mem limit
 and LRU list accounting

On Thu, 2012-11-29 at 17:13 +0100, Jesper Dangaard Brouer wrote:
> The major performance bottleneck on NUMA systems, is the mem limit
> counter which is based an atomic counter.  This patch removes the
> cache-bouncing of the atomic counter, by moving this accounting to be
> bound to each CPU.  The LRU list also need to be done per CPU,
> in-order to keep the accounting straight.
> 
> If fragments belonging together is "sprayed" across CPUs, performance
> will still suffer, but due to NIC rxhashing this is not very common.
> Correct accounting in this situation is maintained by recording and
> "assigning" a CPU to a frag queue when its allocated (caused by the
> first packet associated packet).
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> 
> ---
> V2:
>  - Rename struct cpu_resource -> frag_cpu_limit
>  - Move init functions from inet_frag.h to inet_fragment.c
>  - Cleanup per CPU in inet_frags_exit_net()
> 
>  include/net/inet_frag.h                 |   64 +++++++++++++++++++------------
>  net/ipv4/inet_fragment.c                |   50 ++++++++++++++++++------
>  net/ipv4/ip_fragment.c                  |    3 +
>  net/ipv6/netfilter/nf_conntrack_reasm.c |    2 -
>  net/ipv6/reassembly.c                   |    2 -
>  5 files changed, 80 insertions(+), 41 deletions(-)
> 
> diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
> index 9bbef17..8421904 100644
> --- a/include/net/inet_frag.h
> +++ b/include/net/inet_frag.h
> @@ -1,11 +1,22 @@
>  #ifndef __NET_FRAG_H__
>  #define __NET_FRAG_H__
>  
> +#include <linux/spinlock.h>
> +#include <linux/atomic.h>
> +
> +/* Need to maintain these resource limits per CPU, else we will kill
> + * performance due to cache-line bouncing
> + */
> +struct frag_cpu_limit {
> +	atomic_t                mem;
> +	struct list_head        lru_list;
> +	spinlock_t              lru_lock;
> +} ____cacheline_aligned_in_smp;
> +

This looks like a big patch introducing a specific infrastructure, while
we already have lib/percpu_counter.c

Not counting the addition of a NR_CPUS array, which is really
unfortunate these days.



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