From b49960a05e32121d29316cfdf653894b88ac9190 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 2 May 2012 02:28:41 +0000 Subject: tcp: change tcp_adv_win_scale and tcp_rmem[2] 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: Eric Dumazet Cc: Neal Cardwell Cc: Tom Herbert Cc: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'net/ipv4/tcp.c') diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 8bb6adeb62c..1272a88c2a6 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3243,7 +3243,7 @@ void __init tcp_init(void) { struct sk_buff *skb = NULL; unsigned long limit; - int max_share, cnt; + int max_rshare, max_wshare, cnt; unsigned int i; unsigned long jiffy = jiffies; @@ -3303,15 +3303,16 @@ void __init tcp_init(void) tcp_init_mem(&init_net); /* Set per-socket limits to no more than 1/128 the pressure threshold */ limit = nr_free_buffer_pages() << (PAGE_SHIFT - 7); - max_share = min(4UL*1024*1024, limit); + max_wshare = min(4UL*1024*1024, limit); + max_rshare = min(6UL*1024*1024, limit); sysctl_tcp_wmem[0] = SK_MEM_QUANTUM; sysctl_tcp_wmem[1] = 16*1024; - sysctl_tcp_wmem[2] = max(64*1024, max_share); + sysctl_tcp_wmem[2] = max(64*1024, max_wshare); sysctl_tcp_rmem[0] = SK_MEM_QUANTUM; sysctl_tcp_rmem[1] = 87380; - sysctl_tcp_rmem[2] = max(87380, max_share); + sysctl_tcp_rmem[2] = max(87380, max_rshare); pr_info("Hash tables configured (established %u bind %u)\n", tcp_hashinfo.ehash_mask + 1, tcp_hashinfo.bhash_size); -- cgit v1.2.3-70-g09d2