Access_log off impact on Requests/sec

[stevewin]

Thanks Maxim.

Setting either 'accept_mutex pff;' or reuseport on the listen directive
doesn't seem to change the general trend much

(apologies for formatting below but can't seem to find a way to paste data
elegantly in this forum)


In data below the Columns are as follows

"Wrk_threads"  "Connections" "Default config"  "access_log off';" 
"access_log off; + accept_mutex off;"  "access_log off; +
listen...reuseport"

Requests/sec:
8	8	19352.37	22290.17	23944.48	23448.55
16	16	24839.12	28408.74	26976.59	27545.21
16	24	24845.17	28479.84	27039.90	27631.32
16	32	24633.34	25373.32	22097.93	25792.31
16	48	24540.14	21701.73	19953.71	23836.73
16	72	24620.15	19669.01	19285.64	20222.72
16	96	24591.50	19616.52	19646.13	19669.74
16	120	24569.45	19815.90	19752.29	19818.98
16	200	24642.54	20001.03	19981.29	19974.83
16	300	24161.27	20185.21	20376.75	20381.96
16	400	24607.07	20526.47	20743.34	20459.76
16	500	24712.25	20626.14	21016.65	20927.98
16	1000	24597.04	21137.30	21377.55	21032.03

Average Latency:
8	8	0.87ms	774.84us	348.81us	580.52us
16	16	1.61ms	1.31ms	679.01us	2.14ms
16	24	1.25ms	1.06ms	642.36us	1.52ms
16	32	3.94ms	3.23ms	1.93ms	10.26ms
16	48	8.71ms	5.00ms	3.25ms	26.24ms
16	72	17.21ms	5.37ms	3.95ms	7.53ms
16	96	36.09ms	9.79ms	8.49ms	8.05ms
16	120	44.31ms	12.13ms	9.82ms	9.82ms
16	200	108.02ms	22.18ms	21.58ms	19.26ms
16	300	112.68ms	36.75ms	39.94ms	35.11ms
16	400	94.84ms	58.44ms	60.78ms	53.03ms
16	500	82.97ms	78.26ms	65.91ms	71.37ms
16	1000	50.99ms	164.28ms	156.12ms	165.86ms

Socket errors:
8	8	none	none	none	none
16	16	none	none	none	none
16	24	none	none	none	none
16	32	none	none	none	none
16	48	none	none	none	none
16	72	none	none	none	none
16	96	none	none	none	none
16	120	none	none	none	none
16	200	none	none	none	none
16	300	timeout 35	none	none	none
16	400	 read 14, timeout 44	none	none	none
16	500	 read 37, timeout 111	none	none	 timeout 57
16	1000	timeout 189	timeout 473	timeout 629	timeout 1162


I had been experimenting with various tuning parameters for both NGINX and
Linux including 

NGINX 
 worker_connections, access_log, worker_rlimit_nofile, multi_accept,
keepalive_requests 

Linux
somaxconn, tcp_max_tw_buckets, netdev_max_backlog, tcp_max_syn_backlog,
ip_local_port_range, tcp_fin_timeout, tcp_tw_recycle, tcp_tw_reuse,
wmem_max, tcp_rmem, tcp_wmem

When I was getting undesired results with 'optimiizations' - I started
backing off the various tunings above - for some reason the access log off
seems to be the main perpetrator - for reasons I don't understand

On the client side I'm running on a machine with Intel(R) Xeon(R) CPU
E3-1241 v3 @ 3.50GHz (4 core/ 8 thread).  I've repeated the runs with both 8
and 32 wrk threads with similar trend using access_log off;

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,268609,268622#msg-268622