On 17.11.2011 14:18, Jeremy Chadwick wrote:
On Thu, Nov 17, 2011 at 10:12:10AM +0200, Kostik Belousov wrote:
On Wed, Nov 16, 2011 at 11:59:06PM -0800, Doug Barton wrote:
On 11/16/2011 23:49, Kostik Belousov wrote:
On Wed, Nov 16, 2011 at 10:46:27PM -0800, Doug Barton wrote:
On 11/15/2011 02:09, Jeremy Chadwick wrote:
On Tue, Nov 15, 2011 at 11:07:45AM +0200, Kostik Belousov wrote:
On Mon, Nov 14, 2011 at 12:51:35PM -0800, Doug Barton wrote:
On 11/14/2011 12:31, Doug Barton wrote:
Trying to track down a load problem we're seeing on 8.2-RELEASE-p4 i386
in a busy web hosting environment I came across the following post:
http://lists.freebsd.org/pipermail/freebsd-questions/2011-October/234520.html
That basically describes what we're seeing as well, including the
"doesn't happen on Linux" part.
Does anyone have any ideas about this?
With incredibly similar stuff running on 7.x we didn't see this problem,
so it seems to be something new in 8.
Just took a closer look at our ktrace, and actually our pattern is
slightly different than the one in that post. In ours the second option
is null, but the third is set:
74195 httpd 0.000017 RET sigprocmask 0
74195 httpd 0.000013 CALL sigprocmask(SIG_BLOCK,0,0xbfbf89d4)
74195 httpd 0.000009 RET sigprocmask 0
74195 httpd 0.000013 CALL sigprocmask(SIG_BLOCK,0,0xbfbf89d4)
74195 httpd 0.000009 RET sigprocmask 0
74195 httpd 0.000012 CALL sigprocmask(SIG_BLOCK,0,0xbfbf89d4)
But repeated hundreds of times in a row.
The calls cannot come from rtld, they are generated by some setjmp()
invocation. If signal-safety is not needed, sigsetjmp() should be used
instead.
Quick grep of the apache httpd source shows a single setjmp() in their
copy of pcre. No idea is it to safe to change setjmp() into sigsetjmp(?, 0).
I hate cross-posting, but: adding freebsd-apache@ to the list. Some of
the Apache folks (not just port committers) may have some insight to
Kostik's findings.
Thanks to everyone for the responses. We tried Kostik's suggestion and
unfortunately it didn't reduce the number of sigprocmask() calls to a
statistically significant degree.
Does anyone have any other ideas on ways to debug this? We're sort of
running out of things to test. :-/
Given how important (and prevalent) the Apache + FreeBSD combination is,
I'm kind of disturbed that we're seeing this performance problem, and if
it's something in 8.x that's also in 9.x, it would be better to fix it
prior to 9.0-RELEASE.
Since my guess appeared to be not useful,
Well I wouldn't say that they weren't useful, we eliminated the obvious
candidate. So, "not good news" certainly, but not unhelpful. :)
the way forward is to identify
the location of the call(s) that cause the issue. I suggest compliling
at least apache itself, libc, rtld and libthr (if used) with debugging
information. Then, attach to the running apache worker with the gdb and
Note this part.
set breakpoint on sigprocmask. Several backtraces from the hit breakpoint
should give enough data.
We tried that, and got this:
Loaded symbols for /libexec/ld-elf.so.1
0x28183a5d in accept () from /lib/libc.so.7
(gdb) b sigprocmask
Breakpoint 1 at 0x282d8f84
(gdb) c
Continuing.
no thread to satisfy query
0x28183a5d in accept () from /lib/libc.so.7
(gdb)
It seems your libc has no debugging information.
accept() is the pure syscall wrapper, it cannot call sigprocmask.
If gdb catched the PLT trampoline instead of real accept(), we would
see the rtld frames. So install libc, libthr and rtld with debug.
Also, having debug symbols for apache itself can be useful.
I'd also like to point out that enabling debugging symbols in devel/apr1
will be greatly needed here, not just in www/apache*.
I'm wondering if maybe this is some sort of pthread "thing" going on. A
quick grep -r sigmask of the Apache source turns up some pthread_* bits
pertaining to worker.
Is Apache build using WITH_THREADS? What about devel/apr1?
I don't use worker MPM on any of our boxes, we actually use ITK MPM
solely because of the hosting nature of what we do. I've actually never
seen worker MPM in use on any *IX machine I've been on or administrated,
only prefork. The Apache documentation even mentions that "if you want
stability or compatibility, prefork is the choice", while "if you want
scalability, worker is a better choice"[1]. These sorts of quotes often
shock me given what year it is. :-)
[1]: http://httpd.apache.org/docs/2.0/mpm.html
We use ITK MPM too, but we have big trouble with performance on FreeBSD.
Also, I have to say we can`t use keep-alive connection, so apache
creates new child for each request.
--
С уважением,
Daniil Cherednik
.masterhost
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