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From: Paolo Abeni <pabeni@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>
Cc: netdev <netdev@vger.kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Coco Li <lixiaoyan@google.com>
Subject: Re: [PATCH net-next 09/15] net: increase MAX_SKB_FRAGS
Date: Thu, 03 Feb 2022 17:01:44 +0100	[thread overview]
Message-ID: <0d270dc73553e5deb1a195f4ae84f2795eb1b167.camel@redhat.com> (raw)
In-Reply-To: <20220203015140.3022854-10-eric.dumazet@gmail.com>

On Wed, 2022-02-02 at 17:51 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Currently, MAX_SKB_FRAGS value is 17.
> 
> For standard tcp sendmsg() traffic, no big deal because tcp_sendmsg()
> attempts order-3 allocations, stuffing 32768 bytes per frag.
> 
> But with zero copy, we use order-0 pages.
> 
> For BIG TCP to show its full potential, we increase MAX_SKB_FRAGS
> to be able to fit 45 segments per skb.
> 
> This is also needed for BIG TCP rx zerocopy, as zerocopy currently
> does not support skbs with frag list.
> 
> We have used this MAX_SKB_FRAGS value for years at Google before
> we deployed 4K MTU, with no adverse effect.
> Back then, goal was to be able to receive full size (64KB) GRO
> packets without the frag_list overhead.

IIRC, while backporting some changes to an older RHEL kernel, we had to
increase the skb overhead due to kabi issue.

That caused some measurable regressions because some drivers (e.g.
ixgbe) where not able any more to allocate multiple (skb) heads from
the same page. 

All the above subject to some noise - it's a fainting memory.

I'll try to do some tests with the H/W I have handy, but it could take
a little time due to conflicting scheduling here.

Thanks,

Paolo


  parent reply	other threads:[~2022-02-03 16:01 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-03  1:51 [PATCH net-next 00/15] tcp: BIG TCP implementation Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 01/15] net: add netdev->tso_ipv6_max_size attribute Eric Dumazet
2022-02-03 16:34   ` Jakub Kicinski
2022-02-03 16:56     ` Eric Dumazet
2022-02-03 18:58       ` Jakub Kicinski
2022-02-03 19:12         ` Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 02/15] ipv6: add dev->gso_ipv6_max_size Eric Dumazet
2022-02-03  8:57   ` Paolo Abeni
2022-02-03 15:34     ` Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 03/15] tcp_cubic: make hystart_ack_delay() aware of BIG TCP Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 04/15] ipv6: add struct hop_jumbo_hdr definition Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 05/15] ipv6/gso: remove temporary HBH/jumbo header Eric Dumazet
2022-02-03 18:53   ` Alexander H Duyck
2022-02-03 19:17     ` Eric Dumazet
2022-02-03 19:45       ` Alexander Duyck
2022-02-03 19:59         ` Eric Dumazet
2022-02-03 21:08           ` Alexander H Duyck
2022-02-03 21:41             ` Eric Dumazet
2022-02-04  0:05               ` Alexander Duyck
2022-02-04  0:27                 ` Eric Dumazet
2022-02-04  1:14                   ` Eric Dumazet
2022-02-04  1:48                     ` Eric Dumazet
2022-02-04  2:15                       ` Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 06/15] ipv6/gro: insert " Eric Dumazet
2022-02-03  9:19   ` Paolo Abeni
2022-02-03 15:48     ` Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 07/15] ipv6: add GRO_IPV6_MAX_SIZE Eric Dumazet
2022-02-03  2:18   ` Eric Dumazet
2022-02-03 10:44   ` Paolo Abeni
2022-02-03  1:51 ` [PATCH net-next 08/15] ipv6: Add hop-by-hop header to jumbograms in ip6_output Eric Dumazet
2022-02-03  9:07   ` Paolo Abeni
2022-02-03 16:31     ` Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 09/15] net: increase MAX_SKB_FRAGS Eric Dumazet
2022-02-03  5:02   ` kernel test robot
2022-02-03  5:20     ` Eric Dumazet
2022-02-03  5:31       ` Jakub Kicinski
2022-02-03  6:35         ` Eric Dumazet
2022-02-03  5:23   ` kernel test robot
2022-02-03  5:43   ` kernel test robot
2022-02-03 16:01   ` Paolo Abeni [this message]
2022-02-03 17:26   ` Alexander H Duyck
2022-02-03 17:34     ` Eric Dumazet
2022-02-03 17:56       ` Alexander Duyck
2022-02-03 19:18         ` Jakub Kicinski
2022-02-03 19:20           ` Eric Dumazet
2022-02-03 19:54             ` Eric Dumazet
2022-02-04 10:18         ` David Laight
2022-02-04 15:46           ` Alexander Duyck
2022-02-03  1:51 ` [PATCH net-next 10/15] net: loopback: enable BIG TCP packets Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 11/15] bonding: update dev->tso_ipv6_max_size Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 12/15] macvlan: enable BIG TCP Packets Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 13/15] ipvlan: " Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 14/15] mlx4: support BIG TCP packets Eric Dumazet
2022-02-03 13:04   ` Tariq Toukan
2022-02-03 15:54     ` Eric Dumazet
2022-02-03  1:51 ` [PATCH net-next 15/15] mlx5: " Eric Dumazet
2022-02-03  7:27   ` Tariq Toukan
2022-02-04  4:03   ` kernel test robot

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