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Date:	Mon, 21 Jan 2013 15:58:41 +0800
From:	Li Yu <raise.sail@...il.com>
To:	Tom Herbert <therbert@...gle.com>
CC:	David Laight <David.Laight@...lab.com>, netdev@...r.kernel.org,
	davem@...emloft.net, netdev@...kandruth.co.uk,
	eric.dumazet@...il.com
Subject: Re: [PATCH 0/5]: soreuseport: Bind multiple sockets to the same port

于 2013年01月21日 15:23, Li Yu 写道:
> 于 2013年01月17日 02:22, Tom Herbert 写道:
>>> Hmmm.... do you need that sort of fairness between the threads?
>>>
>> Yes :-)
>>
>>> If one request takes longer than average to process, then you
>>> don't want other requests to be delayed when there are other
>>> idle worker processes.
>>>
>> On a heavily loaded server processing thousands of requests/second,
>> law of large numbers hopefully applies where each connection
>> represents approximately same unit of work.
>>
>
> It seem that these words are reasonable for some scenarios, we
> backported old version of SO_REUSEPORT patch into RHEL6 2.6.32-220.x
> kernel on CDN platform, and result in better balanced
> CPU utility among some haproxy instances.
>
> Also, we did a performance benchmark for old SO_REUSEPORT. It
>
> indeed bring significant improvement for short connections performance
> sometimes, but it also has some performance regression another
> sometimes. I think that problem is random selecting policy, the
> selected result may trigger extra CPU cache misses -- I tried to write
> a SO_BINDCPU patch to directly use RPS/RSS hashed result to select
> listen fd, the performance regression disappear then. but I have send
> it here since I did not implement load balance feature yet ...
> I will send the benchmark results soon.
>

These are results of performance benchmark of old SO_REUSEPORT:

HW of testbed:

Summary:	Dell R720, 2 x Xeon E5-2680 0 2.70GHz, 31.4GB / 32GB 1600MHz DDR3
System:		Dell PowerEdge R720 (Dell 02P51C)
Processors:	2 x Xeon E5-2680 0 2.70GHz 8000MHz FSB (2 sockets x 8 cores 
x 2 threads)
Memory:		31.4GB / 32GB 1600MHz DDR3 == 8 x 4GB, 16 x empty
Network:	Chelsio Communications T420-CR Unified Wire Ethernet Controller
OS:		RHEL Server 6.2 (Santiago) x86_64, 64-bit
BIOS:		Dell 1.0.4 02/21/2012

processes/mode - number of worker processes/listen mode
		
		4/8/16 :  numbers of worker processes, each process is
			  bound on individual processor.

                 listen mode:
		 -s: RHEL6 without any extra patch
		 -r: RHEL6 with SO_REUSEPORT
		 -R: RHEL6 with both SO_REUSEPORT and SO_BINDCPU

64B|1x		- This benchmark suite just is to simulate simple RPC
		  workload. The client sends RPC request first, the
		  server replies a RPC response (I said such a pair of
		  messages is a RPC transaction ), then client send
		  next RPC request to start another new RPC trans.
		
		   64B/1024B : both RPC requests/responses are 64/1024
				bytes length.
		   1x/1024x : each TCP connection has 1 or 1024 RPC
			      trans.

The numbers in below table are represented by 10000 trans per second.

=====================================================================
processes/mode	64B|1x	64B|1024x	1024B|1x	1024B|1024x
=====================================================================
4/-s		18	80		17		78
---------------------------------------------------------------------
4/-r		16	71		15		67
---------------------------------------------------------------------
4/-R		23	96		23		92
---------------------------------------------------------------------
8/-s		18	165		18		160
---------------------------------------------------------------------
8/-r		30	155		29		147
---------------------------------------------------------------------
8/-R		36	185		36		180
---------------------------------------------------------------------
16/-s		15	230		14		220
---------------------------------------------------------------------
16/-r		38	230		38		220
---------------------------------------------------------------------
16/-R		43	230		43		220
---------------------------------------------------------------------

Above data are against RHEL6 2.6.32.279.xx kernel, I also tested 
upstream 3.6.2 kernel with these patches, the results are similar.

Thanks

Yu

>>> Also having the same thread normally collect a request would
>>> make it more likely that the required code/data be in the
>>> cache of the cpu (assuming that the main reason for multiple
>>> threads is to load balance over multiple cpus, and with the
>>> threads tied to a single cpu).
>>>
>> Right.  Multiple listener sockets also imply that the work on the
>> connected sockets will be in the same thread or at least dispatched to
>> thread which is close to the same CPU.  soreuseport moves the start of
>> siloed processing into kernel.
>>
>>> If there are a lot of processes sleeping in accept() (on the same
>>> socket) it might be worth looking at which is actually woken
>>> when a new connection arrives. If they are sleeping in poll/select
>>> it is probably more difficult (but not impossible) to avoid waking
>>> all the processes for every incoming connection.
>>
>> We had considered solving this within accept.  The problem is that
>> there's no way to indicate how much work a thread should do via
>> accept.  For instance, an event loop usually would look like:
>>
>> while (1) {
>>      fd = accept();
>>      process(fd);
>> }
>>
>> With multiple threads, the number of accepted sockets in a particular
>> thread is non-deterministic.  It is even possible that one thread
>> could end up accepting all the connections, and the others are starved
>> (wake up but no connection to process.).  Since connections are the
>> unit of work, this creates imbalance among threads.  There was an
>> attempt to fix this in user space by sleeping for a while instead of
>> calling accept on threads for one that have already have a
>> disproportionate number of connections.  This was unpleasant-- it
>> needed shared state in user space and provided no granularity.
>>
>
> I also have some thinks on this imbalance problem ...
>
> At Last, I assumed that every accept-thread holds same numbers of
> listen sockets, so we just can do load balance base on length of accept
> queue.
>
> Thanks for great SO_REUSEPORT work.
>
>> Tom
>> --
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>

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