1. 21 5月, 2012 1 次提交
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  3. 03 5月, 2012 1 次提交
    • E
      tcp: change tcp_adv_win_scale and tcp_rmem[2] · b49960a0
      Eric Dumazet 提交于
      tcp_adv_win_scale default value is 2, meaning we expect a good citizen
      skb to have skb->len / skb->truesize ratio of 75% (3/4)
      
      In 2.6 kernels we (mis)accounted for typical MSS=1460 frame :
      1536 + 64 + 256 = 1856 'estimated truesize', and 1856 * 3/4 = 1392.
      So these skbs were considered as not bloated.
      
      With recent truesize fixes, a typical MSS=1460 frame truesize is now the
      more precise :
      2048 + 256 = 2304. But 2304 * 3/4 = 1728.
      So these skb are not good citizen anymore, because 1460 < 1728
      
      (GRO can escape this problem because it build skbs with a too low
      truesize.)
      
      This also means tcp advertises a too optimistic window for a given
      allocated rcvspace : When receiving frames, sk_rmem_alloc can hit
      sk_rcvbuf limit and we call tcp_prune_queue()/tcp_collapse() too often,
      especially when application is slow to drain its receive queue or in
      case of losses (netperf is fast, scp is slow). This is a major latency
      source.
      
      We should adjust the len/truesize ratio to 50% instead of 75%
      
      This patch :
      
      1) changes tcp_adv_win_scale default to 1 instead of 2
      
      2) increase tcp_rmem[2] limit from 4MB to 6MB to take into account
      better truesize tracking and to allow autotuning tcp receive window to
      reach same value than before. Note that same amount of kernel memory is
      consumed compared to 2.6 kernels.
      Signed-off-by: NEric Dumazet <edumazet@google.com>
      Cc: Neal Cardwell <ncardwell@google.com>
      Cc: Tom Herbert <therbert@google.com>
      Cc: Yuchung Cheng <ycheng@google.com>
      Acked-by: NNeal Cardwell <ncardwell@google.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      b49960a0
  4. 30 4月, 2012 1 次提交
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  21. 29 3月, 2012 1 次提交