Apache 1.3 + PHP 5 on FreeBSD 6 -- bad performance under load

BSD bsdlists at celeritystorm.com
Wed Feb 15 08:15:30 PST 2006


Hello list,

I've been having trouble identifying what's causing my apache server to 
take about 5 seconds to reply to new http requests.

The machine in question is a Dual Xeon 2.8GHz with 4GB RAM, running 
apache 1.3.33_4 and PHP5 on 6.0-RELEASE-p4. It is a very busy PHP-based 
site.

I have done a lot of tweaking on this server, but when the load goes a 
bit higher, it'll take about 5 seconds to answer to a standard GET / 
HTTP/1.1 via telnet (no PHP involved, since I'm not sending valid HTTP 
headers and it will reply with a 400 bad request).

It is a problem with apache, as telnetting to the sshd port and hitting 
ENTER yields an instant "Protocol mismatch". -- no delay whatsoever.

Both CPUs are around 65% idle after some PHP tweaks, so it's not CPU 
starvation either.

I have accept filters enabled on the kernel, and apache is using them; also:

options         KVA_PAGES=768
options         PMAP_SHPGPERPROC=5120

- to avoid that "colleting PV entries - suggest increasing 
PMAP_SHPGPERPROC".

So far I've been unable to pinpoint what's causing apache a ~5 sec delay 
to process the GET. A timestamped tcpdump shows the following:

Establishing the connection:
02/15/2006 16:06:44.232973 192.168.0.1.53578 > APACHE_SERVER.80: S 
3958791824:3958791824(0) win 65535 <mss 1460,nop,wscale 
1,nop,nop,timestamp 7596496 0> (DF) [tos 0x10]
02/15/2006 16:06:44.387141 APACHE_SERVER.80 > 192.168.0.1.53578: S 
2261546731:2261546731(0) ack 3958791825 win 65535 <mss 1460,nop,wscale 
2,nop,nop,timestamp 1124627170 7596496> (DF)
02/15/2006 16:06:44.387348 192.168.0.1.53578 > APACHE_SERVER.80: . ack 1 
win 33304 <nop,nop,timestamp 7596512 1124627170> (DF) [tos 0x10]

02/15/2006 16:06:44.536819 APACHE_SERVER.80 > 192.168.0.1.53578: . ack 1 
win 32942 <nop,nop,timestamp 1124627318 7596512> (DF)


GET: (note: delay from previous step was induced by manually switching 
terminals and typing)
02/15/2006 16:06:49.148143 192.168.0.1.53578 > APACHE_SERVER.80: P 
1:17(16) ack 1 win 33304 <nop,nop,timestamp 7596988 1124627318> (DF) 
[tos 0x10]
02/15/2006 16:06:49.395079 APACHE_SERVER.80 > 192.168.0.1.53578: . ack 
17 win 32938 <nop,nop,timestamp 1124632177 7596988> (DF)
02/15/2006 16:06:49.395284 192.168.0.1.53578 > APACHE_SERVER.80: P 
17:19(2) ack 1 win 33304 <nop,nop,timestamp 7597013 1124632177> (DF) 
[tos 0x10]
02/15/2006 16:06:49.642127 APACHE_SERVER.80 > 192.168.0.1.53578: . ack 
19 win 32937 <nop,nop,timestamp 1124632423 7597013> (DF)


"400 bad request" reply:
02/15/2006 16:06:59.769277 APACHE_SERVER.80 > 192.168.0.1.53578: P 
1:481(480) ack 19 win 32942 <nop,nop,timestamp 1124642548 7597013> (DF)
02/15/2006 16:06:59.769453 APACHE_SERVER.80 > 192.168.0.1.53578: F 
481:481(0) ack 19 win 32942 <nop,nop,timestamp 1124642548 7597013> (DF)
02/15/2006 16:06:59.769543 192.168.0.1.53578 > APACHE_SERVER.80: . ack 
482 win 33064 <nop,nop,timestamp 7598050 1124642548> (DF) [tos 0x10]
02/15/2006 16:06:59.770548 192.168.0.1.53578 > APACHE_SERVER.80: F 
19:19(0) ack 482 win 33304 <nop,nop,timestamp 7598050 1124642548> (DF) 
[tos 0x10]
02/15/2006 16:06:59.923720 APACHE_SERVER.80 > 192.168.0.1.53578: . ack 
20 win 32941 <nop,nop,timestamp 1124642703 7598050> (DF)


As you can see, it took 10 seconds to reply to the GET, yet the 
accepting of the connection was instant.
I have more than enough maxfiles, maxproc, maxfilesperproc, nmbclusters 
etc. I guess the connection is so promptly answered because of the http 
accept filters built in the kernel.

As a final note, the MaxClients I'm using are not nearly enough (around 
200 connections/second, according to pfstat graphics vs MaxClients 98). 
The reason for this is that trying to match MaxClients with the real 
load resulted in two 0.0% idle processors, since the PHP code is a bit 
heavy. I've opted to disable KeepAlive and lower MaxClients instead. 
Could this be the delay I'm seeing ? I think so, but I need more 
opinions, so feel free to reply.




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