Chapter 4 Performance Test Result with Packet Dropper

In this chapter, we will introduce packet dropper, both random dropping version and regular dropping version.

4.1 Random Dropping

On receiving each packet, the Dropper checks the destination IP address. If the destination is the target IP, we get a 16-bit random number, if the random number is less than the dropping threshold value which is rate*65535, we drop this packet, otherwise, process it normally.

The random number is generated in this way. Because the assembly instruction “rdtsc” is specific to Intel processor, this way is only good for it.

Get a CPU cycle

unsigned l, h;

__asm__ volatile("rdtsc": "=a" (l), "=d" (h));

Get the lower 16 bit from the CPU cycle. Swap the lower byte with the higher byte.

In the following calculation:

The AVG refers to the average value of 10 times’ experiments result (either elapse time or number of packet dropped).

The Var is the variation of the 10 times’ experiment result.

It is:  sqrt( ( (t1-avg)**2 + (t2-avg)**2 + .....+ (t10-avg)**2 )/10) Where ti is the experiment result (either elapse time or number of packets dropped). And i is 1…10.

The throughput is:  1526*100000/ AVG

Figure 4.1 shows the relation chart of throughput and dropping rate.

Table 4.1 shows the detail data of the test result.

Drop Rate	1st	2nd	3rd	4th	5th	6th	7th	8th	9th	10th	AVG	VAR	Throughput(B/s)
0.000	12.32	12.31	12.31	12.31	12.31	12.31	12.31	12.31	12.31	12.31	12.311	0.003	12395419
0.004	12.58	12.59	12.60	12.78	12.40	12.59	12.79	12.79	12.59	12.59	12.630	0.117	12082344
0.008	13.63	13.43	13.22	13.92	13.21	13.78	13.81	13.40	14.38	14.37	13.715	0.402	11126504
0.012	14.93	14.43	16.20	15.59	15.91	16.09	16.76	15.41	15.60	15.98	15.690	0.629	9725940
0.016	18.21	17.94	16.63	18.59	18.19	15.77	18.68	16.64	18.65	18.91	17.821	1.026	8562932
0.020	19.03	19.29	21.32	20.36	18.80	20.64	20.73	22.64	21.26	19.39	20.346	1.159	7500246
0.024	23.72	25.32	22.86	23.00	23.81	26.15	23.38	24.46	22.97	23.08	23.875	1.055	6391623
0.028	27.50	27.87	30.08	27.19	28.50	31.01	27.45	33.13	32.90	30.96	29.659	2.155	5145150
0.032	34.62	37.09	35.42	37.10	31.75	33.26	29.71	33.38	35.41	35.08	34.282	2.198	4451316
0.036	40.21	36.55	38.61	37.46	39.47	36.10	43.48	40.70	39.05	42.04	39.367	2.224	3876343
0.040	47.50	43.83	49.85	48.76	51.44	50.21	48.39	48.02	51.76	46.92	48.668	2.222	3135531
0.044	57.63	58.25	56.20	58.41	60.10	57.71	59.47	61.01	63.59	57.05	58.942	2.064	2588986
0.048	60.53	62.69	60.53	62.10	60.77	64.72	69.53	63.17	61.82	64.32	63.018	2.585	2421530
0.052	69.94	71.16	77.68	71.36	81.50	78.39	75.87	83.58	80.62	72.28	76.238	4.610	2001627
0.056	81.00	81.88	87.80	88.41	80.69	83.04	86.63	82.62	82.11	83.47	83.765	2.672	1821763
0.060	94.69	88.28	85.34	98.35	100.85	91.36	93.02	100.69	91.31	99.59	94.348	5.138	1617416
0.064	102.81	113.83	112.53	119.74	118.44	107.60	111.76	101.93	108.02	110.67	110.733	5.584	1378090
0.068	128.40	118.65	107.80	123.88	121.82	122.60	129.09	121.18	132.55	120.71	122.668	6.459	1244008
0.072	137.22	140.05	129.92	136.85	142.88	138.54	133.10	148.12	135.43	143.60	138.571	5.066	1101241
0.076	149.76	138.79	158.41	152.24	167.07	154.32	150.96	164.03	154.89	157.76	154.823	7.489	985642
0.080	157.50	168.43	172.89	171.53	184.27	166.37	155.31	173.43	160.68	160.15	167.056	8.432	913466
0.084	194.28	196.97	186.59	181.34	190.61	189.30	193.47	201.84	206.89	194.90	193.619	6.964	788146
0.088	209.22	205.81	224.02	217.21	214.00	216.19	227.36	210.13	207.06	221.41	215.241	6.975	708973
0.092	228.31	220.76	224.77	241.97	223.95	229.48	227.43	213.72	205.09	230.78	224.626	9.485	679351
0.096	250.06	252.02	270.32	248.97	244.95	237.94	249.31	249.61	266.07	307.15	257.640	18.789	592299
0.100	268.61	275.46	280.16	279.69	283.42	268.90	288.08	253.52	274.59	271.92	274.435	9.147	556052
0.104	317.36	276.15	307.06	292.50	310.21	326.06	321.80	330.96	318.36	305.04	310.550	15.630	491386
0.108	325.51	344.83	340.28	295.20	302.02	334.39	327.88	351.86	285.12	306.06	321.315	21.620	474923
0.112	359.97	352.99	353.36	370.75	352.03	347.78	319.44	353.36	346.82	375.23	353.173	14.319	432083
0.116	405.68	385.94	393.06	419.70	373.77	391.31	379.12	370.57	368.25	387.88	387.528	15.269	393778
0.120	426.30	422.77	401.62	424.46	426.22	376.22	420.19	400.01	418.08	403.23	411.910	15.461	370469
0.124	446.80	508.11	445.87	503.94	491.30	440.11	444.95	435.18	460.41	464.42	464.109	25.861	328802
0.128	486.39	469.44	539.99	473.81	467.21	535.21	497.34	466.53	506.08	434.08	487.608	31.134	312956
0.132	527.16	532.07	586.13	511.39	543.10	536.87	563.76	492.69	491.36	546.67	533.120	28.166	286239
0.136	600.00	566.77	558.85	608.03	556.17	592.22	558.70	579.79	570.13	625.97	581.663	22.720	262351
0.140	644.62	616.15	631.62	633.08	633.37	624.63	579.93	594.24	594.61	572.06	612.431	24.013	249171
0.144	692.91	616.93	645.45	626.70	630.92	643.30	628.59	767.10	695.61	683.01	663.052	44.209	230148
0.148	720.46	696.01	706.25	703.32	717.07	744.12	728.69	675.32	713.80	724.99	713.003	18.108	214024

Table 4.1 Performance result of random packet dropping

Figure 4.1 Performance Curve of Random dropping

Through /proc file system, we can see the actual number of TCP packets that are dropped. Table 5.2 shows the packet loss.

The IDEAL is the ideal number of packets dropped during the experiments with a specific dropping rate.

 The deviation is (IDEAL - AVG)/IDEAL

Drop Rate	1st	2nd	3rd	4th	5th	6th	7th	8th	9th	10th	AVG	VAR	IDEAL	DEV
0.000	0	0	0	0	0	0	0	0	0	0	0	0	0	0.000
0.004	392	403	409	366	381	407	424	418	414	370	398	19	402	-0.008
0.008	840	864	814	842	785	812	861	814	774	797	820	29	806	0.017
0.012	1214	1200	1198	1229	1235	1227	1205	1191	1237	1191	1213	17	1215	-0.002
0.016	1674	1606	1598	1635	1661	1621	1566	1672	1662	1684	1638	37	1626	0.007
0.020	2087	2056	2003	2081	2019	2097	2003	2007	1972	2047	2037	40	2041	-0.002
0.024	2521	2480	2552	2465	2396	2583	2468	2418	2449	2458	2479	55	2459	0.008
0.028	2794	3029	2845	2857	2824	2868	2881	3003	2927	2859	2889	72	2881	0.003
0.032	3312	3333	3247	3320	3246	3274	3310	3216	3420	3334	3301	55	3306	-0.001
0.036	3827	3682	3766	3693	3607	3648	3835	3792	3763	3741	3735	72	3734	0.000
0.040	4204	4153	4196	4186	4274	4247	4121	4241	4231	4218	4207	43	4167	0.010
0.044	4589	4604	4646	4675	4602	4577	4639	4772	4738	4553	4640	67	4603	0.008
0.048	4873	5070	5011	5069	4940	4990	5203	4947	5056	5094	5025	89	5042	-0.003
0.052	5418	5573	5629	5366	5582	5497	5530	5674	5501	5430	5520	92	5485	0.006
0.056	5968	6009	5961	6055	5834	5833	5928	5946	5814	5791	5914	86	5932	-0.003
0.060	6307	6441	6375	6468	6454	6375	6308	6276	6423	6347	6377	64	6383	-0.001
0.064	6722	6866	6823	6873	7029	6859	6926	6780	6711	7033	6862	106	6838	0.004
0.068	7427	7325	7056	7346	7313	7287	7325	7202	7379	7429	7309	105	7296	0.002
0.072	7712	7846	7572	7802	7727	7879	7811	7734	7768	7764	7762	81	7759	0.000
0.076	8217	8206	8371	8384	8315	8264	8163	8369	8249	8175	8271	79	8225	0.006
0.080	8496	8726	8652	8690	8815	8718	8523	8825	8763	8670	8688	104	8696	-0.001
0.084	9487	9263	9250	9197	9325	9188	9333	9219	9189	9263	9271	87	9170	0.011
0.088	9733	9820	9672	9619	9854	9906	9666	9733	9751	9806	9756	86	9649	0.011
0.092	10184	10175	10195	10297	10167	10132	10193	10067	9974	10291	10168	91	10132	0.003
0.096	10650	10612	10899	10644	10607	10674	10718	10476	10744	10752	10678	106	10619	0.005
0.100	11185	11268	10985	11324	11158	11127	11158	11185	11003	11209	11160	99	11111	0.004
0.104	11888	11621	11557	11810	11731	11811	11890	11840	11612	11606	11737	121	11607	0.011
0.108	12226	12187	12329	12120	12147	12328	12026	12218	12084	12099	12176	96	12108	0.006
0.112	12687	12707	12818	12793	12623	12826	12555	12737	12708	12968	12742	110	12613	0.010
0.116	13371	13215	13102	13361	13265	13061	13321	13222	13111	13192	13222	103	13122	0.008
0.120	13968	13859	13857	13893	13895	13690	13962	13651	13894	13686	13836	111	13636	0.015
0.124	14342	14444	14443	14563	14688	14505	14331	14334	14330	14389	14437	113	14155	0.020
0.128	14801	14781	14965	14999	14790	15046	15006	14716	14853	14657	14861	128	14679	0.012
0.132	15512	15429	15634	15257	15419	15592	15293	15346	15322	15687	15449	143	15207	0.016
0.136	15752	15881	16198	16112	16067	15917	15868	16144	16007	16005	15995	133	15741	0.016
0.140	16654	16292	16725	16609	16633	16638	16405	16552	16522	16614	16564	122	16279	0.018
0.144	17166	16893	17095	17004	16839	16998	16720	17209	16888	17138	16995	151	16822	0.010
0.148	17740	17630	17515	17664	17515	17566	17392	17570	17424	17671	17569	105	17371	0.011

Table 4.2 Number of packets dropped by router (Dublin)

4.2 Regular Dropping

On receiving each packet, the Dropper checks the destination IP address. If the destination is the target IP, we increment the counter, if the counter equals to cutoff (an integer), we drop this packet, otherwise, process it normally.

/******************************************************* packet_dropper

* this is what dev_queue_xmit will call while this module is installed *********/

unsigned rate = 6;

static unsigned int count = 0;

unsigned number_of_packet_dropped=0;

int packet_dropper(struct sk_buff *skb) {

if (skb->nh.iph->daddr == target) {

count ++;

if ( count == rate)

{

count = 0;

number_of_packet_dropped++;

return 1;

}

}

return 0; /* continue with normal routine */

} /* packet_dropper */

The source code is

http://www.cs.unh.edu/cnrg/lin/linuxProject/phase3/regular_dropper/

Figure 4.2 Performance curve of regular dropping.

Figure 4.2 shows the performance after the regular packet dropper is applied on the router.

Table 4.3 shows the experiment detail data. In Table 4.3, column “cutoff” means “drop 1 packet out of every cutoff packets”. For the original data, see http://www.cs.unh.edu/cnrg/lin/linuxProject/phase2/nov5Tcp/

Experiment on packet_dropper. packets are dropped one out of every 1/rate packets
drop rate	cutoff	Elapse time ( sec ) Tcp request size 1448 bytes, iteration time 100000												Throughput(B/s)
		1st	2nd	3rd	4th	5th	6th	7th	8th	9th	10th	AVG	Var
0	-	12.33	12.31	12.31	12.31	12.31	12.31	12.31	12.31	12.31	12.31	12.312	0.004	12394411.96
0.0001	10000	12.33	12.32	12.32	12.32	12.32	12.32	12.32	12.32	12.32	12.32	12.321	0.002	12385358.33
0.0005	2000	12.34	12.33	12.33	12.33	12.33	12.33	12.33	12.33	12.33	12.33	12.331	0.002	12375314.25
0.001	1000	12.36	12.35	12.35	12.35	12.35	12.35	12.35	12.39	12.36	12.35	12.356	0.008	12350275.17
0.002	500	12.40	12.39	12.39	12.39	12.39	12.39	12.39	12.39	12.39	12.39	12.391	0.002	12315390.20
0.004	250	12.39	12.38	12.38	12.38	12.38	12.38	12.38	12.38	12.38	12.38	12.381	0.002	12325337.21
0.006	166	12.40	12.39	12.39	12.39	12.39	12.39	12.39	12.39	12.39	12.39	12.391	0.002	12315390.20
0.008	125	12.43	12.42	12.42	12.42	12.42	12.42	12.42	12.42	12.42	12.42	12.421	0.002	12285645.28
0.01	100	12.45	12.45	12.44	12.44	12.44	12.50	12.45	12.45	12.45	12.45	12.452	0.010	12255059.43
0.02	50	12.59	12.58	12.58	12.58	12.58	12.58	12.58	12.58	12.58	12.58	12.581	0.002	12129401.48
0.03	33	12.92	12.73	12.71	12.78	12.71	12.84	13.04	12.78	12.72	12.74	12.797	0.082	11924669.84
0.04	25	14.02	13.96	13.95	13.94	13.96	13.95	14.14	13.96	13.93	13.96	13.977	0.041	10917936.61
0.05	20	14.36	14.34	14.33	14.32	14.53	14.32	14.33	14.33	14.35	14.33	14.354	0.036	10631182.95
0.06	16	15.12	15.16	15.11	15.10	15.12	15.12	15.11	15.10	15.10	15.11	15.115	0.012	10095931.19
0.07	14	15.56	15.67	15.54	15.47	15.53	15.47	15.47	15.48	15.52	15.44	15.515	0.049	9835642.93
0.08	12	16.30	16.06	16.06	16.26	16.07	16.06	16.28	16.07	16.06	16.27	16.149	0.103	9449501.52
0.09	11	15.92	15.75	15.93	15.73	15.93	15.75	15.94	15.74	15.95	15.72	15.836	0.098	9636271.79
0.10	10	15.79	15.42	15.58	15.81	15.43	15.61	15.42	15.77	15.61	15.41	15.585	0.133	9791466.15
0.11	9	15.79	15.41	15.78	15.62	15.42	15.79	15.43	15.59	15.80	15.41	15.604	0.152	9779543.71
0.12	8	16.66	17.06	17.63	17.83	15.88	16.08	16.46	16.43	17.25	15.89	16.717	0.580	9128432.13
0.13	7	15.51	15.30	15.70	15.30	15.49	15.30	15.49	15.49	15.50	15.30	15.438	0.110	9884700.09

Table 4.3 Performance of regular dropping

Figure 4.3 shows that given the same dropping rate, the regular dropping has a much better performance than the random dropping.

Figure 4.3 Performance comparison of random dropping and regular dropping.

4.3 Interesting Result on Regular Dropping

When we set regular dropping rate to 1/6 (regularly drop one packet out of every 6 packets). The elapse time varies significantly. Sometimes it takes only a few seconds to send 50000 packets. Sometimes it takes hundreds of seconds to finish it. And sometimes it even takes thousands of seconds to do that. Table 4.4 shows the experiment data.

Iteration Times	Time elapse (Second)
	1^st	2^nd	3^rd	4^th	5^th	6^th	7^th	8^th	9^th	10^th	Random
											1^st	2^nd
10000	1.77	12.73	1.77	1.77	1.78	1.77	1.77	346.65	1.78	1.77	122.34	114.58
20000	3.35	3.35	3.35	3.35	3.34	3.34	3.34	3.34	3.34	455.36	181.67	189.52
30000	4.91	4.92	4.92	4.92	1971.68	4.92	652.67	….....			313.62	328.32
40000	6.45	6.45	6.45	6.44	6.45	1129.76	….....				385.51	392.27
50000	8.01	1597.12	8.01	1008.76	566.48	8.01	….....				611.35	528.09
60000	9.58	9.57	9.57	2006.39	2993.67	9.60	….....				583.14	614.00
70000	10.95	4946.53	1128.08	4944.91	….....						779.36	824.49
80000	12.71	12.71	4000.19	211.84	….....						765.21	819.63

Table 4.4 Elapse time when regular dropping rate is set 1/6