netdev - Re: [PATCH net-next] tcp: speedup tcp_fixup

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Date:	Thu, 16 May 2013 15:20:06 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ncardwell@...gle.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org, ycheng@...gle.com
Subject: Re: [PATCH net-next] tcp: speedup tcp_fixup_rcvbuf()

From: Neal Cardwell <ncardwell@...gle.com>
Date: Thu, 16 May 2013 11:23:03 -0400

> On Thu, May 16, 2013 at 1:25 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> From: Eric Dumazet <edumazet@...gle.com>
>>
>> tcp_fixup_rcvbuf() contains a loop to estimate initial socket
>> rcv space needed for a given mss. With large MTU (like 64K on lo),
>> we can loop ~500 times and consume a lot of cpu cycles.
>>
>> perf top of 200 concurrent netperf -t TCP_CRR
>>
>> 5.62%  netperf  [kernel.kallsyms]  [k] tcp_init_buffer_space
>> 1.71%  netperf  [kernel.kallsyms]  [k] _raw_spin_lock
>> 1.55%  netperf  [kernel.kallsyms]  [k] kmem_cache_free
>> 1.51%  netperf  [kernel.kallsyms]  [k] tcp_transmit_skb
>> 1.50%  netperf  [kernel.kallsyms]  [k] tcp_ack
>>
>> Lets use a 100% factor, and remove the loop.
>>
>> 100% is needed anyway for tcp_adv_win_scale=1
>> default value, and is also the maximum factor.
>>
>> Refs: commit b49960a05e32
>>       ("tcp: change tcp_adv_win_scale and tcp_rmem[2]")
>>
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
 ...
> Acked-by: Neal Cardwell <ncardwell@...gle.com>

Applied.
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