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The Reliable, High Performance TCP/HTTP Load Balancer


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Willy TARREAU


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2009/08/23 - Quick test of version 1.4-dev2 : barrier of 100k HTTP req/s crossed

Introduction

    It was my first test since I moved house. I wanted to quickly plug the machines together to see if my work on version 1.4 went into the right direction, and most importantly was not causing performance drops. Verdict below confirms it. A new record of 108000 HTTP requests processed per second was broken, and a new record of 40000 forwarded HTTP requests per second was broken too.

    The first test only accepts a new connection, reads the request, parses it, checks an ACL, sends a redirect and closes. A session rate of 132000 connections per second could even be measured in pure TCP mode, but this is not very useful :
    .

    The second test forwards the request to a real server instead, and fetches a 64-byte object :

    These improvements are due to the ability to tell the system to merge some carefully chosen TCP packets at critical phases of the session. This results in lower number of packets per session, which in turn saves both bandwidth and CPU cycles. The smallest session is now down to 5-6 packets on each side, down from 9 initially.

2009/04/18 - New benchmark of HAProxy at 10 Gbps using Myricom's 10GbE NICs (Myri-10G PCI-Express)

Introduction

    Precisely one year ago I ran some tests on the high performance 10GbE NICs that were donated to me by Myricom. In one year, haproxy has evolved quite a lot. The I/O subsystem has been completely reworked and it can now make use of the TCP splicing implemented in Linux 2.6 to avoid copying data in userspace. This test will show what is possible with TCP splicing now.

Lab setup

    The lab has almost not changed. One of the two AMD systems was upgraded to a Phenom X4 running at 3 GHz, but that's all. Haproxy will still be run on the intel Core2Duo E8200 at 2.66 GHz. The kernels were updated to 2.6.27-wt5 which is 2.6.27.19 + a few patches that I need to easily boot those machines from the network. The 2.6.27 kernel includes support for TCP splicing, for generic Large Receive Offload (LRO) and also includes a more recent myri10ge driver which now has no problem moving 10 Gbps of traffic on the AMD boards in both directions. The kernel has received fixes for bugs in the splicing code that were spotted a few months ago while preparing this test. It seems everyone is not lucky enough to run tests on such fantastic hardware, so bugs are to be expected in such configurations ;-)

    Hardware / software setup :
    MachineRoleMoboCPUKernelmyri drvmyri fwsoftware
    AMD2ClientASUS M3A32MVPAMD Phenom X4/3GHz2.6.27smp-wt51.4.3-1.3581.4.36inject31
    C2DProxyASUS P5Eintel C2D E8200/2.66GHz2.6.27smp-wt51.4.3-1.3581.4.36haproxy-1.3.17-12
    AMD1ServerASUS M3A32MVPAMD X2/3.2GHz2.6.27smp-wt51.4.3-1.3581.4.36httpterm 1.3.0

    The tests are quite simple. An HTTP request generator runs on the faster Phenom (amd2) since this soft is the heaviest of the chain. HAProxy runs on the Core2Duo (c2d). The web server runs on the smaller Athlon (amd1). Connections are point-to-point since I still have no 10GbE switch (donations accepted ;-)). Haproxy is configured to use kernel splicing in the response path :

    	listen http-splice
    		bind	:8000
    		option	splice-response
    		server	srv1 1.0.0.2:80
    	      

    Here is a photo of the machines connected together.

Tests methodology

    A script calls the request generator for object size from 64 bytes to 10 megs. The request generator continuously connects to HAProxy to fetch the selected object from the server in loops for 1 minute, with 500 to 1000 concurrent connections. Statistics are collected every second, so we have 60 measures. The 5 best ones are arbitrarily eliminated because they may include some noise. The next 20 best ones are averaged and used as the test's result. This means that the 35 remaining values are left unused. This is not a problem because they include values collected during ramping up/down. In practise, tests show that using 20 to 40 values report the same results. Note that network bandwidth is measured at the HTTP level and does not account for TCP acks nor TCP headers. Other captures at the network level show slightly higher throughput.
    The collected values are then passed to another script which produces a GNUPLOT script, which when run, produces a PNG graph. The graph shows in green the number of hits per second, which also happens to be the connection rate since haproxy does only one hit per connection. In red, we have the data rate (HTTP headers+data only) reached for each object size. In general, the larger the object, the smaller the connection overhead and the higher the bandwidth.

Tests in single-process mode, 8kB buffers, TCP splicing, LRO enabled, Jumbo frames

    In this test, we configure haproxy to use the kernel's splicing feature to directly forward the HTTP response from the server to the client without copying data. The network interfaces MTU default to jumbo frames (9000 bytes). Large Receive Offload (LRO) is enabled by default on these NICs too, which results in larger segments being processed at once. Both network interrupts are sent to CPU core 1, and haproxy is running alone on CPU core 0. This is how I have achieved the highest throughput to date. A total of 19 objects sizes from 64 bytes to 10 MB have been tested :
    We can see that now even with only one haproxy process we have no problem reaching the 10 Gbps. Network measures have shown 9.950 Gbps of forwarded traffic on the client interface for all object sizes larger than 1 MB, which was not possible at all in earlier version without the help of kernel-based TCP splicing. Also the session rate has increased a lot to reach a peak of 38628 sessions/s as seen on the stats page below during the test. This is 55% more than one year ago on the same hardware ! One can notice that the gigabit is reached for objects larger than about 4kB, which is a lot better than what is observed with more common gigabit NICs.

    The CPU usage has dropped a lot since the introduction of LRO and TCP splicing. Forwarding 9.95 Gbps of Ethernet traffic consumes less than 20% of the CPU :

    	root@c2d:tmp# vmstat 1
    	procs                      memory      swap          io     system       cpu
    	r  b  w   swpd   free   buff  cache   si   so    bi    bo    in    cs  us sy id
    	1  0  0      0 1951376   3820  19868    0    0     0     0 25729 23965  1 15 84
    	0  0  0      0 1950652   3820  19868    0    0     0     0 25744 23818  3 17 80
    	0  0  0      0 1950632   3820  19868    0    0     0     0 25720 24652  1 18 80
    	0  0  0      0 1949512   3820  19868    0    0     0     0 25531 24047  3 16 81
    	1  0  0      0 1948484   3820  19868    0    0     0     0 25911 22706  2 19 79
    	0  0  0      0 1949388   3820  19868    0    0     0     0 26189 23757  3 15 82
    	1  0  0      0 1948460   3820  19868    0    0     0     0 25811 23766  1 20 79
    	      

Tests in single-process mode, 8kB buffers, TCP splicing, LRO enabled, standard frames

    Most people cannot enable jumbo frames on the client side because they're connected to the Internet and the 'Net is not jumbo-friendly. However, since haproxy is a proxy, it can be used as a jumbo frame converter, reserving jumbo frames for the internal network, while the external network runs at 1500. This test has been performed with MTU=1500 on the client network.
    A hole is observed around 10 kB. In fact, it is at 7kB. This is the largest HTTP response that can fit in a single buffer when haproxy is built with 8kB buffers. The effect is not really a drop of performance above 10kB, but a performance boost below 8kB. Indeed, when haproxy get a full response in a single read, it can save several system calls and push the response to the client without ever polling. Note that at these sizes, kernel splicing is not used at all, yet we're almost at 2Gbps for 10kB objects. We're still very close to 10 Gbps on large objects. We measured 8.55 Gbps of HTTP traffic, and the network monitoring tools have measured 9.2 Gbps of ethernet traffic on the 1500-byte MTU interface (that was 746000 packets per second).

    Concerning the CPU usage, at full load (9.2 Gbps at 1500-byte frames), the CPU usage was extremely low : 2% user, 15% system. That means that the LRO feature of the Myri-10G NIC is extremely efficient at offloading the system :

    	root@c2d:tmp# vmstat 1
    	procs                      memory      swap          io     system       cpu
    	r  b  w   swpd   free   buff  cache   si   so    bi    bo    in    cs  us sy id
    	0  0  0      0 1811764   3820  19844    0    0     0     0 26289 19089  2 14 84
    	0  0  0      0 1787924   3820  19844    0    0     0     0 26268 19578  1 13 86
    	1  0  0      0 1772704   3820  19844    0    0     0     0 26288 18517  3 13 84
    	0  0  0      0 1774260   3820  19848    0    0     0     0 26284 19522  2 15 83
    	1  0  0      0 1766144   3820  19848    0    0     0     0 26260 19042  3 15 83
    	1  0  0      0 1734412   3820  19848    0    0     0     0 26270 18603  4 15 81
    	0  0  0      0 1719864   3820  19848    0    0     0     0 26294 18886  1 14 85
    	    

Session setup/teardown rates

    It is interesting to see how many sessions setup/teardown haproxy supports in various modes. This is important for people who want to protect against attacks for example, or support extreme loads. First test consisted in modelizing an ACL blocking requests at the TCP inspection stage :
    	      acl blacklist src 1.0.0.0/8
    	      tcp-request content reject if blacklist
    	    
    Note that this filter applies before HTTP request parsing. Well, the result was beyond my expectations, I had to use the two AMD systems to attack haproxy to get a score, but I couldn't saturate the CPU, which remained below 75% used. The session rate has broken the symbolic 100k/s barrier with 105931 sessions per second !

HTTP session rate

    Many other people are interested in the HTTP session rate on the client side. The difference with previous test is that we have to completely parse the HTTP request before taking a decision. There are a number of circumstances where a client request may not be routed to a server after being parsed. This happens when the request is invalid, blocked by ACLs or redirected to an external server. So in order to make the test the most representative of real usage, the configuration has been set to perform a redirect when an ACL detects that the local servers are being shut down for maintenance :

    	      acl service_down nbsrv -lt 2
    	      redirect prefix http://backup.site if service_down
    	    
    The session rate was still very high : 82702 HTTP requests per second with about 20% CPU remaining available (eg for logging) :

    What's really interesting here is that the user CPU usage oscillates between 23 and 30%, meaning that the HTTP parser takes less than one third of a core to process 82700 requests/s. This extrapolates to a potential of about 250-300000 HTTP requests per second being processed when keep-alive is supported. Of course this does not take into account the added work induced by network traffic.

Conclusion

    The first conclusion of those three tests is that the Linux 2.6 kernel, the Myri10GE driver and HAProxy have improved a lot since last year's tests. It is now possible to run at 10GbE line rate with one single process without consuming much CPU power, with or without jumbo frames, and that's a great news. 10GbE becomes mature. Some tests on various NICs tend to indicate that the kernel splicing is not always interesting, especially with dumb NICs. But the carefully designed ones really benefit from this feature. The Myri-10G NIC certainly is one of those. David Miller, the maintainer of the Linux networking says that Sun's Neptune chip is another excellent one. I have not had the opportuniy to give it a try though. Anyway, I would only recommend such well-designed NICs to anyone who seriously considers switching to 10GbE speeds on a single machine. Large objects are still required to fill 10GbE (at least 1MB average). That is totally compatible with file sharing or online videos. For people with a mixed traffic, targetting 3-4 Gbps with files averaging around 30 kB would be more realistic (which is still 15-20000 sessions per second).

    Another nice feature set is haproxy's ability to act as an MTU converter for 10GbE networks. Alteon did that 10 years ago to permit 1500 and 9000 bytes MTU to coexist on gigabit networks. Now the same issue happens with 10GbE. Some servers will be set to use jumbo frames but the outer networks will not support them. Setting haproxy in full transparent mode between two interfaces should help a lot. Note that the same could be true for IPv6/IPv4 translation at full line rate.

- revisit last year's benchmarks
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