How can I configure Apache to use more of my CPU?
14,094
To configure Apache to use more of your CPU, you need to get rid of the bottle-neck that is currently preventing Apache from using more CPU. Because requests are taking 3-8 seconds to complete, you know there is some sort of bottle-neck, you need to find it.
Things to look at are:
- Determine if the Apache host is the bottle-neck. If you run
uptimewhile requests are taking 3-8 seconds, does the load show as being high (in the double or triple digits)? You can't really read a lot into this, because a high load could mean the problem exists elsewhere, but if the load is low while requests are taking 3-8 seconds it probably is a remote issue. - If you have resources required by this service on other machines, such as a database, check the system load there as well.
- Look at the output of "vmstat 1" on the server. This will show system utilization statistics, updated every second. Things to look at are "cpu wa" (if it's double digits it probably means the disc is saturated), and "swap si/so" (if these are non-zero it means you are out of memory), and "cpu id" (idle CPU time, if this is <10 your CPU is saturated). If "cpu sy" time is high, that may indicate that you are forking too much (perhaps Apache MaxRequests is too low?) or other kernel-level overhead. Press Control-C to end the "vmstat 1" output.
- You can run "strace -p [AN APACHE PROCEED ID]" to get an idea of what the Apache processes are doing. This shows the system calls they are making, but if you aren't familiar with system calls you can sometimes get information just by reading the output as text. For example, last week I had a server that was acting like yours and the strace would pause for several seconds with the last thing that was displayed was a log message, and I tracked it down to a PHP file that was sending a bunch of log messages to syslog.
If you don't have "munin" installed, you probably should. If you do, look at the graphs to see how the system utilization changes when the system is responding slowly and when it's working well. If you see jumps in the graphs, those might indicate where the bottle-neck is. If you see blank areas in all the graphs, that probably means the system is saturated. If only the Apache graphs are blank, it probably means that Apache has reached it's max connections, probably a side-effect of the performance problems.
Also note that if you have multiple CPUs, but you have a single-threaded application like Zope sitting behind Apache, it could be that one of your CPUs is saturated where the others are idle. If you press "1" in top, that will show you the utilization of each individual core. Look for one that is at 0% idle all the time, where the others are much more idle.
Using these techniques I've been able to isolate and resolve most performance problems similar to this.
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DevOps & SysAdmins: How can I configure Apache to use more of my CPU? (2 Solutions!!)
Author by
Ryan
Updated on September 18, 2022Comments
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Ryan over 1 year
Apache threads are stacking up on one of my web servers (300-500 simultaneous requests, some taking 3-8s to process!), but CPU usage is very low (~10%). Page load time is slowing way down as a result. I have plenty of idle CPU power. How can I use more of it to handle these threads faster?
Here's the top of top...
Tasks: 469 total, 1 running, 468 sleeping, 0 stopped, 0 zombie Cpu(s): 8.1% us, 1.7% sy, 0.0% ni, 90.3% id, 0.0% wa, 0.0% hi, 0.0% si Mem: 9181012k total, 7998772k used, 1182240k free, 0k buffers Swap: 0k total, 0k used, 0k free, 0k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 11351 apache 15 0 364m 30m 17m S 11.9 0.3 0:00.73 httpd 7527 apache 15 0 365m 36m 23m S 8.6 0.4 0:01.76 httpd 7607 apache 16 0 364m 35m 22m S 2.3 0.4 0:01.47 httpd 11498 apache 17 0 359m 19m 11m S 2.3 0.2 0:00.07 httpd 11497 apache 16 0 362m 23m 13m S 1.7 0.3 0:00.05 httpd 1840 apache 15 0 366m 44m 29m S 1.3 0.5 0:03.74 httpd 5358 apache 15 0 364m 36m 24m S 1.3 0.4 0:02.58 httpd 8090 apache 15 0 365m 31m 17m S 1.3 0.3 0:01.10 httpd 11346 apache 15 0 361m 28m 18m S 1.3 0.3 0:00.12 httpd 4051 apache 16 0 365m 40m 27m S 1.0 0.5 0:01.72 httpd 32575 apache 16 0 365m 42m 28m S 0.7 0.5 0:03.62 httpd 5145 apache 16 0 365m 37m 24m S 0.7 0.4 0:02.23 httpd 8173 apache 16 0 363m 35m 23m S 0.7 0.4 0:00.29 httpd 5466 apache 15 0 365m 31m 18m S 0.3 0.4 0:01.18 httpd 7420 apache 16 0 364m 36m 23m S 0.3 0.4 0:01.24 httpd 11485 apache 16 0 362m 23m 12m S 0.3 0.3 0:00.04 httpd 1 root 15 0 10272 612 584 S 0.0 0.0 0:02.78 init 30129 root 16 -4 12536 400 396 S 0.0 0.0 0:00.00 udevd 30402 root 16 0 5840 580 480 S 0.0 0.0 0:14.01 syslogd 30414 rpc 18 0 7992 408 404 S 0.0 0.0 0:00.00 portmap 30439 root 18 0 10088 548 544 S 0.0 0.0 0:00.00 rpc.statd 30478 memcache 15 0 141m 5364 516 S 0.0 0.1 1:16.34 memcached 30496 root 16 0 60604 744 636 S 0.0 0.0 0:07.31 sshd 30507 root 15 0 21572 796 688 S 0.0 0.0 0:04.56 xinetd 31817 root 15 0 166m 932 860 S 0.0 0.0 0:00.03 httpsd 31820 psaadm 15 0 175m 7992 4596 S 0.0 0.1 0:02.31 httpsd 31924 root 15 0 19704 924 552 S 0.0 0.0 0:02.50 crond 13316 root 16 0 98528 3628 2796 S 0.0 0.0 0:00.01 sshd 1655 root 19 0 8600 1180 972 S 0.0 0.0 0:00.00 mysqld_safe 1695 mysql 16 0 4268m 464m 4684 S 0.0 5.2 10:05.19 mysqld 32564 root 16 0 98528 3612 2780 S 0.0 0.0 0:00.00 sshd 28489 root 15 0 98528 3628 2796 S 0.0 0.0 0:00.00 sshd 32152 root 16 0 98528 3612 2780 S 0.0 0.0 0:00.01 sshd 5781 root 15 0 98528 3628 2796 S 0.0 0.0 0:00.01 sshd 7801 root 17 0 356m 11m 5472 S 0.0 0.1 0:05.74 httpd 7804 apache 16 0 366m 36m 21m S 0.0 0.4 0:00.35 httpd 7805 apache 16 0 370m 31m 13m S 0.0 0.4 0:00.11 httpd 8172 apache 15 0 366m 34m 19m S 0.0 0.4 0:00.62 httpd 9430 apache 16 0 365m 45m 32m S 0.0 0.5 0:02.67 httpd 11393 apache 16 0 363m 37m 25m S 0.0 0.4 0:00.75 httpd 11551 apache 17 0 360m 31m 22m S 0.0 0.4 0:00.24 httpd 32345 apache 16 0 364m 39m 27m S 0.0 0.4 0:02.86 httpd 32472 apache 16 0 394m 70m 27m S 0.0 0.8 0:03.77 httpd 32488 apache 16 0 364m 42m 29m S 0.0 0.5 0:02.38 httpd 32501 apache 16 0 365m 41m 28m S 0.0 0.5 0:01.71 httpd 32644 apache 16 0 365m 36m 23m S 0.0 0.4 0:01.79 httpd 32765 apache 15 0 364m 39m 26m S 0.0 0.4 0:02.65 httpd 1334 apache 16 0 368m 42m 26m S 0.0 0.5 0:02.77 httpd 1339 apache 15 0 362m 39m 29m S 0.0 0.4 0:01.84 httpd 1351 apache 15 0 364m 43m 30m S 0.0 0.5 0:02.59 httpd 1553 apache 16 0 363m 41m 29m S 0.0 0.5 0:02.74 httpd 1555 apache 16 0 365m 37m 24m S 0.0 0.4 0:01.59 httpd 1564 apache 15 0 365m 40m 27m S 0.0 0.5 0:01.88 httpd 1569 apache 16 0 364m 35m 22m S 0.0 0.4 0:00.63 httpd 1573 apache 15 0 367m 39m 24m S 0.0 0.4 0:01.66 httpd 1575 apache 16 0 363m 36m 24m S 0.0 0.4 0:01.88 httpd 1583 apache 16 0 364m 34m 21m S 0.0 0.4 0:01.92 httpd 1594 apache 15 0 367m 44m 29m S 0.0 0.5 0:03.71 httpd 1689 apache 15 0 365m 38m 24m S 0.0 0.4 0:01.47 httpd 1690 apache 15 0 365m 39m 26m S 0.0 0.4 0:01.18 httpd 1710 apache 16 0 363m 34m 23m S 0.0 0.4 0:00.99 httpd 1725 apache 15 0 364m 39m 26m S 0.0 0.4 0:01.80 httpd 1726 apache 16 0 365m 40m 26m S 0.0 0.5 0:00.90 httpd 1737 apache 16 0 364m 30m 17m S 0.0 0.3 0:00.46 httpd 1919 apache 15 0 363m 34m 22m S 0.0 0.4 0:00.83 httpd 1930 apache 16 0 364m 33m 21m S 0.0 0.4 0:00.50 httpd 1934 apache 15 0 364m 40m 27m S 0.0 0.5 0:02.20 httpdAnd critical httpd.conf settings:
Timeout 120 KeepAlive On MaxKeepAliveRequests 200 KeepAliveTimeout 3 <IfModule prefork.c> StartServers 8 MinSpareServers 5 MaxSpareServers 20 ServerLimit 256 MaxClients 256 MaxRequestsPerChild 4000 </IfModule> <IfModule worker.c> StartServers 2 MaxClients 150 MinSpareThreads 25 MaxSpareThreads 75 ThreadsPerChild 25 MaxRequestsPerChild 0 </IfModule>-
ceejayoz over 12 yearsAre you sure CPU is your bottleneck?
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ravi yarlagadda over 12 yearsWhich MPM are you using? And what's its config look like?
StartServers,ServerLimit, etc.? -
Ryan over 12 years@ShaneMadden I just added some confs above. Does that help? (BTW, Thanks for taking a look)
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ceejayoz over 12 yearsAre you sure Apache is your bottleneck and not, say, PHP code, or MySQL locking, etc.?
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ravi yarlagadda over 12 years@Ryan Run
apache2ctl -lto figure out which one's in use. And as ceejayoz mentioned, definitely check disk, databases, network throughput, etc as potential sources of bottlenecks. -
Zoredache over 12 yearsWhy do you have no swap, and why is your cache at 0k? That is pretty unusual.
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MShoubaki over 12 yearsYour point about being able to rule out the CPU as the bottle-neck is a good one. Otherwise, your message could be more helpful: References to the other apache performance Q&As, what information is missing from the httpd.conf file, you ask a lot of questions, without providing information on how Ryan can get those answers.
