From: Eric Dumazet <eric.dumazet@gmail.com>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>,
netdev@vger.kernel.org, davem@davemloft.net,
jeffrey.t.kirsher@intel.com, Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH 2/2] net: Update alloc frag to reduce get/put page usage and recycle pages
Date: Thu, 12 Jul 2012 07:06:41 +0200 [thread overview]
Message-ID: <1342069601.3265.8218.camel@edumazet-glaptop> (raw)
In-Reply-To: <4FFE303F.8070902@gmail.com>
On Wed, 2012-07-11 at 19:02 -0700, Alexander Duyck wrote:
> The gain will be minimal if any with the 1500 byte allocations, however
> there shouldn't be a performance degradation.
>
> I was thinking more of the ixgbe case where we are working with only 256
> byte allocations and can recycle pages in the case of GRO or TCP. For
> ixgbe the advantages are significant since we drop a number of the
> get_page calls and get the advantage of the page recycling. So for
> example with GRO enabled we should only have to allocate 1 page for
> headers every 16 buffers, and the 6 slots we use in that page have a
> good likelihood of being warm in the cache since we just keep looping on
> the same page.
>
Its not possible to get 16 buffers per 4096 bytes page.
sizeof(struct skb_shared_info)=0x140 320
Add 192 bytes (NET_SKB_PAD + 128)
Thats a minimum of 512 bytes (but ixgbe uses more) per skb.
In practice for ixgbe, its :
#define IXGBE_RXBUFFER_512 512 /* Used for packet split */
#define IXGBE_RX_HDR_SIZE IXGBE_RXBUFFER_512
skb = netdev_alloc_skb_ip_align(rx_ring->netdev, IXGBE_RX_HDR_SIZE)
So 4 buffers per PAGE
Maybe you plan to use IXGBE_RXBUFFER_256 or IXGBE_RXBUFFER_128 ?
next prev parent reply other threads:[~2012-07-12 5:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-12 0:18 [PATCH 1/2] tcp: Fix out of bounds access to tcpm_vals Alexander Duyck
2012-07-12 0:18 ` [PATCH 2/2] net: Update alloc frag to reduce get/put page usage and recycle pages Alexander Duyck
2012-07-12 0:29 ` Eric Dumazet
2012-07-12 1:11 ` David Miller
2012-07-12 2:02 ` Alexander Duyck
2012-07-12 5:06 ` Eric Dumazet [this message]
2012-07-12 15:33 ` Alexander Duyck
2012-07-12 0:32 ` [PATCH 1/2] tcp: Fix out of bounds access to tcpm_vals David Miller
2012-07-12 1:46 ` Alexander Duyck
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