netdev - Re: [PATCH net-next] net/mlx4: use one page fragment per incoming frame

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Date:	Mon, 03 Jun 2013 11:05:41 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>
Subject: Re: [PATCH net-next] net/mlx4: use one page fragment per incoming
 frame

On 06/03/2013 10:54 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> mlx4 driver has a suboptimal memory allocation strategy for regular
> MTU=1500 frames, as it uses two page fragments :
>
> One of 512 bytes and one of 1024 bytes.
>
> This makes GRO less effective, as each GSO packet contains 8 MSS instead
> of 16 MSS.
>
> Performance of a single TCP flow gains 25 % increase with the following
> patch.
 >
> Before patch :
>
> A:~# netperf -H 192.168.0.2 -Cc
> MIGRATED TCP STREAM TEST ...
> Recv   Send    Send                          Utilization       Service Demand
> Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
> Size   Size    Size     Time     Throughput  local    remote   local   remote
> bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB
>
>   87380  16384  16384    10.00      13798.47   3.06     4.20     0.436   0.598
>
> After patch :
>
> A:~# netperf -H 192.68.0.2 -Cc
> MIGRATED TCP STREAM TEST ...
> Recv   Send    Send                          Utilization       Service Demand
> Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
> Size   Size    Size     Time     Throughput  local    remote   local   remote
> bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB
>
>   87380  16384  16384    10.00      17273.80   3.44     4.19     0.391   0.477


I take it this is a > 10 Gbit/s NIC?

What if any is the downside to an incoming stream of small packets?

rick jones

> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Amir Vadai <amirv@...lanox.com>
> ---
>   drivers/net/ethernet/mellanox/mlx4/mlx4_en.h |    6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> index b1d7657..b1f51c1 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> +++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> @@ -98,11 +98,11 @@
>   #define MLX4_EN_ALLOC_SIZE	PAGE_ALIGN(16384)
>   #define MLX4_EN_ALLOC_ORDER	get_order(MLX4_EN_ALLOC_SIZE)
>
> -/* Receive fragment sizes; we use at most 4 fragments (for 9600 byte MTU
> +/* Receive fragment sizes; we use at most 3 fragments (for 9600 byte MTU
>    * and 4K allocations) */
>   enum {
> -	FRAG_SZ0 = 512 - NET_IP_ALIGN,
> -	FRAG_SZ1 = 1024,
> +	FRAG_SZ0 = 1536 - NET_IP_ALIGN,
> +	FRAG_SZ1 = 4096,
>   	FRAG_SZ2 = 4096,
>   	FRAG_SZ3 = MLX4_EN_ALLOC_SIZE
>   };
>
>
> --
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