netdev - Re: [PATCH RFC] net: decrease the length of backlog queue immediately after it's detached from sk

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Date:	Mon, 11 Apr 2016 22:42:41 +0800
From:	Yang Yingliang <yangyingliang@...wei.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
CC:	<netdev@...r.kernel.org>, <dingtianhong@...wei.com>
Subject: Re: [PATCH RFC] net: decrease the length of backlog queue immediately
 after it's detached from sk



On 2016/4/9 1:04, Eric Dumazet wrote:
> On Fri, 2016-04-08 at 12:53 -0400, David Miller wrote:
>> From: Eric Dumazet <eric.dumazet@...il.com>
>> Date: Fri, 08 Apr 2016 07:44:25 -0700
>>
>>> On Fri, 2016-04-08 at 19:18 +0800, Yang Yingliang wrote:
>>>
>>>> I expand  tcp_adv_win_scale and tcp_rmem. It has no effect.
>>>
>>> Try :
>>>
>>> echo -2 >/proc/sys/net/ipv4/tcp_adv_win_scale
>>>
>>> And restart your flows.
>>
>> I'm honestly beginning to suspect a bug in their driver and how they
>> handle skb->truesize.
>>
>> Yang, until you show us the driver you are using and how is handles
>> receive packets, we are largely in the dark about a major component
>> of this issue and that is entirely unfair to us.
>
> Apparently their skb->truesize and skb->len combinations are correct.
>
> I suspect an issue with rcvbuf autouning on a bidirectional tcp traffic.
> We mostly focus on unidirectional flows, but they seem to use a mixed
> case.
>
> Also, fact that sendmsg() locks the socket for the duration of the call
> is problematic : I suspect their issues would mostly disappear by using
> smaller chunk sizes (ie 64KB per sendmsg() instead of 256KB).
It's less packets dropping with using 64KB chunk.

>
> We also could add resched points in sendmsg() (processing backlog if it
> gets too hot), but I fear this would slow down the fast path.
>
>
>
>
>