netdev - Re: 200 millisecond timeouts in TCP

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Message-ID: <AANLkTinhb-5T2FqJ6jtgCckT4C69ilGLXrdAy4RcacLe@mail.gmail.com>
Date:	Sat, 5 Jun 2010 07:55:41 +0900
From:	Ryousei Takano <ryousei@...il.com>
To:	Satoru SATOH <satoru.satoh@...il.com>
Cc:	Ivan Novick <novickivan@...il.com>, netdev@...r.kernel.org
Subject: Re: 200 millisecond timeouts in TCP

Hi satoru,

On Sat, Jun 5, 2010 at 12:02 AM, Satoru SATOH <satoru.satoh@...il.com> wrote:
> It's possible to tune the RTO min value (rto_min) per route since
> 2.6.23+.  (see also the manual of iproute2, ip(8) )
>
Yeah, I forgot it.  Per route configuration is a nice idea compared
with global sysctls.

Thanks!
Ryousei

> - satoru
>
> On Fri, Jun 04, 2010 at 03:58:57PM +0900, Ryousei Takano wrote:
>> On Fri, Jun 4, 2010 at 7:37 AM, Ivan Novick <novickivan@...il.com> wrote:
>> > Hello,
>> >
>> > Using tcpdump and systemtap I am seeing that sometimes retransmission
>> > of data is sent after waiting 200 milliseconds.  However sometimes
>> > retransmissions happen quicker.
>> >
>> > Is there a specifc event that causes these 200 milisec delays to kick
>> > in?  Are those events identifiable in netstat -s output?
>> >
>> > Also do you know if the timeout numbers for TCP are configurable parameters?
>> >
>> The minimum RTO value is fixed to 200 ms.  It is useful to make the min/max
>> RTO values tunable.  For example, reducing the minimum RTO value is effective
>> for TCP incast problem [1].  Of course, it may occur spurious retransmissions.
>>
>> [1] Vijay Vasudevan, et al, Safe and Effective Fine-grained TCP Retransmissions
>> for Datacenter Communication, SIGCOMM2009
>>
>> In Solaris, there are two tunable parameters: tcp_rexmit_interval_min/max.
>>
>> Do you have plan to introduce sysctl parameters like these to the Linux.
>>
>> Thanks,
>> Ryousei
>
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