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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Ben Hutchings <bhutchings@solarflare.com>
Cc: David Miller <davem@davemloft.net>,
	netdev@vger.kernel.org, linux-net-drivers@solarflare.com
Subject: Re: [PATCH net-next 3/9] sfc: Increase size of RX SKB header area
Date: Tue, 16 Jul 2013 10:33:55 -0700	[thread overview]
Message-ID: <1373996035.6097.5.camel@edumazet-glaptop> (raw)
In-Reply-To: <1372104801.1896.32.camel@bwh-desktop.uk.level5networks.com>

On Mon, 2013-06-24 at 21:13 +0100, Ben Hutchings wrote:
> From: Jon Cooper <jcooper@solarflare.com>
> 
> This allows the SKB to hold the headers without reallocation more often.
> 
> Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
> ---
>  drivers/net/ethernet/sfc/rx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
> index b915e09..6efff3d 100644
> --- a/drivers/net/ethernet/sfc/rx.c
> +++ b/drivers/net/ethernet/sfc/rx.c
> @@ -36,7 +36,7 @@
>  #define EFX_RECYCLE_RING_SIZE_NOIOMMU (2 * EFX_RX_PREFERRED_BATCH)
>  
>  /* Size of buffer allocated for skb header area. */
> -#define EFX_SKB_HEADERS  64u
> +#define EFX_SKB_HEADERS  128u
>  
>  /* This is the percentage fill level below which new RX descriptors
>   * will be added to the RX descriptor ring.
> 

This patch brings performance decrease for tunnels, because it pulls
into skb->head 128 bytes worth of data.

This includes TCP payload, so GRO or TCP coalescing code is less
effective. Each MSS spans 2 memory areas (small part on skb->head,
remaining on the fragment) : GRO packets have only 8 MSS worth of data,
instead of 16.

The fix would be to allocate 128 bytes in skb->head to prevent future
reallocations of skb->head, but pull 64 bytes only.

  reply	other threads:[~2013-07-16 17:33 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-06-24 20:11 Pull request: sfc-next 2013-06-24 Ben Hutchings
2013-06-24 20:12 ` [PATCH net-next 1/9] sfc: Fix EEH with legacy interrupts Ben Hutchings
2013-06-24 20:13 ` [PATCH net-next 2/9] sfc: Enable RX checksum offload for packets not handled by GRO Ben Hutchings
2013-06-24 20:13 ` [PATCH net-next 3/9] sfc: Increase size of RX SKB header area Ben Hutchings
2013-07-16 17:33   ` Eric Dumazet [this message]
2013-07-16 17:53     ` Ben Hutchings
2013-07-16 20:22       ` Eric Dumazet
2013-07-16 20:57         ` Ben Hutchings
2013-06-24 20:13 ` [PATCH net-next 4/9] sfc: Report software timestamping capabilities Ben Hutchings
2013-06-24 20:14 ` [PATCH net-next 5/9] sfc: Enable accelerated RFS on vlans Ben Hutchings
2013-06-24 20:14 ` [PATCH net-next 6/9] sfc: Define and set RX buffer flag for packets parsed as TCP Ben Hutchings
2013-06-24 20:14 ` [PATCH net-next 7/9] sfc: Do not pass non-TCP packets into GRO code Ben Hutchings
2013-06-24 20:15 ` [PATCH net-next 8/9] sfc: Fix IRQ cleanup in case of a probe failure Ben Hutchings
2013-06-24 20:15 ` [PATCH net-next 9/9] sfc: Improve test for IOMMU in use Ben Hutchings
2013-06-25 23:12 ` Pull request: sfc-next 2013-06-24 David Miller

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