netdev - Re: [RFC PATCH net-next 0/5] tcp: TCP tracer

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Date:	Mon, 15 Dec 2014 17:17:23 -0500
From:	rapier <rapier@....edu>
To:	Tom Herbert <therbert@...gle.com>, Josef Bacik <jbacik@...com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Laurent Chavey <chavey@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Martin KaFai Lau <kafai@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lawrence Brakmo <brakmo@...com>,
	Kernel Team <Kernel-team@...com>
Subject: Re: [RFC PATCH net-next 0/5] tcp: TCP tracer

The Web10g development team at PSC (we've been working with
a number of other organizations on this) will be submitting
the kernel instrument set tomorrow morning. We'd be happy to
join any discussion then.

Chris rapier

On 12/15/14, 5:01 PM, Tom Herbert wrote:
> On Mon, Dec 15, 2014 at 8:42 AM, Josef Bacik <jbacik@...com> wrote:
>> On 12/15/2014 11:03 AM, Eric Dumazet wrote:
>>>
>>> On Sun, 2014-12-14 at 22:55 -0800, Alexei Starovoitov wrote:
>>>
>>>> I think patches 1 and 3 are good additions, since they establish
>>>> few permanent points of instrumentation in tcp stack.
>>>> Patches 4-5 look more like use cases of tracepoints established
>>>> before. They may feel like simple additions and, no doubt,
>>>> they are useful, but since they expose things via tracing
>>>> infra they become part of api and cannot be changed later,
>>>> when more stats would be needed.
>>>> I think systemtap like scripting on top of patches 1 and 3
>>>> should solve your use case ?
>>>> Also, have you looked at recent eBPF work?
>>>> Though it's not completely ready yet, soon it should
>>>> be able to do the same stats collection as you have
>>>> in 4/5 without adding permanent pieces to the kernel.
>>>
>>>
>>> So it looks like web10g like interfaces are very often requested by
>>> various teams.
>>>
>>> And we have many different views on how to hack this. I am astonished by
>>> number of hacks I saw about this stuff going on.
>>>
>>> What about a clean way, extending current TCP_INFO, which is both
>>> available as a getsockopt() for socket owners and ss/iproute2
>>> information for 'external entities'
>>>
>>> If we consider web10g info needed, then adding a ftrace/eBPF like
>>> interface is simply yet another piece of code we need to maintain,
>>> and the argument of 'this should cost nothing if not activated' is
>>> nonsense since major players need to constantly monitor TCP metrics and
>>> behavior.
>>>
>>> It seems both FaceBook and Google are working on a subset of web10g.
>>>
>>> I suggest we meet together and establish a common ground, preferably
>>> after Christmas holidays.
>>>
>>
>> We've set up something for exactly this case at the end of January but have
>> yet to get a response from Google.  If any of the Google people cc'ed (or
>> really anybody, its not a strictly FB/Google thing) is interested please
>> email me directly and I'll send you the details, we will be meeting face to
>> face in the bay area at the end of January.  Thanks,
>>
>
> Maybe this would be good for discussion at netdev01?
>
>> Josef
>>
>>
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