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From: Neal Cardwell <ncardwell@google.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "David Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	"Tom Herbert" <therbert@google.com>,
	"Maciej Żenczykowski" <maze@google.com>,
	"Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi>
Subject: Re: [PATCH net-next] tcp: introduce tcp_try_coalesce
Date: Mon, 23 Apr 2012 21:13:58 -0400	[thread overview]
Message-ID: <CADVnQyngwym7z_zSi8h2U_1e_wVCwGMPZScywWFWM2AYvxyqjw@mail.gmail.com> (raw)
In-Reply-To: <1335201102.5205.28.camel@edumazet-glaptop>

On Mon, Apr 23, 2012 at 1:11 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> commit c8628155ece3 (tcp: reduce out_of_order memory use) took care of
> coalescing tcp segments provided by legacy devices (linear skbs)
>
> We extend this idea to fragged skbs, as their truesize can be heavy.
>
> ixgbe for example uses 256+1024+PAGE_SIZE/2 = 3328 bytes per segment.
>
> Use this coalescing strategy for receive queue too.
>
> This contributes to reduce number of tcp collapses, at minimal cost, and
> reduces memory overhead and packets drops.

The mechanics look solid, but I'm a little concerned about the
potential added overhead for the new case where tcp_try_coalesce()
does a skb_copy_bits() for in-order data that it is coalescing at the
end of the sk_receive_queue. Do you have any performance numbers for
this case to help suggest whether this added copy is a concern?

neal

  reply	other threads:[~2012-04-24  1:13 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-23 17:11 [PATCH net-next] tcp: introduce tcp_try_coalesce Eric Dumazet
2012-04-24  1:13 ` Neal Cardwell [this message]
2012-04-24  2:13   ` Eric Dumazet
2012-04-24  2:29     ` Eric Dumazet
2012-04-24  2:39 ` Neal Cardwell
2012-04-24  2:46   ` David Miller
2012-04-24  2:59     ` Eric Dumazet
2012-04-24  3:34     ` [PATCH net-next] tcp: tcp_try_coalesce returns a boolean Eric Dumazet
2012-04-24  3:37       ` David Miller

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