Date: Fri, 30 May 1997 19:42:43 -0700 From: Julian Elischer <julian@whistle.com> Cc: julian@alpo.whistle.com, hackers@freebsd.org Subject: WHy does Appache eat my system? Message-ID: <338F9023.41C67EA6@whistle.com>
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I've been doing some kernel profiling on a freeBSD system, trying
to figure out why I have 0% idle and 60% in the kernel.
I haven't tracked it all down but here are a few bits of the
traces...
Apache seems to be the main culprit.
does anyoen who really knows apache heve any suggestions?
---------begin Kernel syscall trace extract-----
10077 httpd 865038863.248455 RET read 8192/0x2000
10077 httpd 865038863.249045 CALL break(0x13e000)
10077 httpd 865038863.249476 RET break 0
10077 httpd 865038863.249817 CALL break(0x140000)
10077 httpd 865038863.250209 RET break 0
10077 httpd 865038863.250547 CALL break(0x142000)
10077 httpd 865038863.250936 RET break 0
10077 httpd 865038863.251277 CALL break(0x144000)
10077 httpd 865038863.251665 RET break 0
10077 httpd 865038863.252005 CALL break(0x146000)
10077 httpd 865038863.252394 RET break 0
10077 httpd 865038863.252732 CALL break(0x148000)
10077 httpd 865038863.253117 RET break 0
10077 httpd 865038863.253454 CALL break(0x14a000)
10077 httpd 865038863.254057 RET break 0
10077 httpd 865038863.254463 CALL break(0x14c000)
10077 httpd 865038863.254860 RET break 0
10077 httpd 865038863.255196 CALL break(0x14e000)
10077 httpd 865038863.255579 RET break 0
### this continues for a while
10077 httpd 865038863.312158 CALL break(0x1e6000)
10077 httpd 865038863.312546 RET break 0
10077 httpd 865038863.312879 CALL break(0x1e8000)
10077 httpd 865038863.313263 RET break 0
10077 httpd 865038863.313598 CALL break(0x1ea000)
---------end extract--
'break' is the 'brk()' syscall.
This occurs apparently on every request..
it's just spent about 60 msec doing basically nothing but
picking up 8K pages of memeory from the kernel.
I can't help thinking that this must be able to be made better.
when the request is serviced, it is ALL thrown back. and the next
request goes and fetches it again.
A dump of a kernel execution profile at the same time
shows the following:
--begin extract---------------------------------------------
13.23 63.35 614785/614785 _Xsyscall [2]
[3] 78.1 13.23 63.35 614785 _syscall [3]
2.61 19.49 415263/415263 _obreak [4]
0.52 10.42 47275/47275 _read [7]
0.26 4.45 17514/17514 _write [17]
0.07 4.63 7122/7122 _stat [18]
1.13 3.39 9210/9210 _select [19]
0.11 3.82 6206/6206 _open [23]
2.87 0.00 613302/671847 _generic_copyin[29]
0.05 0.73 5868/5868 _fstat [77]
0.09 0.61 8722/8722 _flock [79]
0.01 0.65 937/937 _lstat [87]
0.05 0.60 7391/7391 _close [88]
---end extract--
this shows that 19% of all system time was being spent in obreak()
(which is the brk() syscall.)
over a 100 second period there were 415263 calls to it
(4000 per second?) which nearly all came from apache.
Has anyone done anything on this?
our system is limited to 6 servers so each is doing 800
brk() calls per second!(in fact in my traces they are nearly
all done by a couple of the servers. I am also tracking more
such innefficiencies, but this is the obvious one to start
with :)
If not I will work on it and make the results available but
I hate to duplicate work by others.
julian
(julian@freebsd.org, julian@whistle.com)
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