Edit report at http://bugs.php.net/bug.php?id=52569&edit=1
ID: 52569
Comment by: mplomer at gmx dot de
Reported by: mplomer at gmx dot de
Summary: Implement "ondemand" process-manager (to allow zero
children)
Status: Analyzed
Type: Feature/Change Request
Package: FPM related
PHP Version: 5.3.3
Assigned To: fat
Block user comment: N
New Comment:
Some test results of the "ondemand"-pm:
General
- Pool has to start with 0 children - OK
- Handling and checking of new config options - OK
Concurrent requests
- Children has to be forked immediately on new requests without delay -
OK
- Idle children has to be killed after pm.process_idle_timeout + 0-1s -
OK
- When there are more than one idle children, kill only one per second
PER POOL - OK
Reaching pm.max_children limit
- No more processes has to be created - OK
- Requests have to wait until one child becomes idle and then get
handled immediately without further delay - OK
- When limit is reached, issue a warning and increase status counter
(and do this only once) - OK:
Aug 28 13:39:41.537174 [WARNING] pid 27540,
fpm_pctl_on_socket_accept(), line 507: [pool www] server reached
max_children setting (10), consider raising it
- Warning is re-issued after children count decreases and hit the limit
again - OK
CPU burns
- When reaching max_children limit, pause libevent callback and reenable
it in the maintenance routine, to avoid CPU burns - OK
- When children takes too long to accept() the request, avoid CPU burn -
NOTOK
-> happens sometimes (in praxis only sometimes after forking) - to
reproduce add an usleep(50000) in children's code after fork(), or
apachebench with ~200 concurrent requests :-)
-> You get a lot of: "fpm_pctl_on_socket_accept(), line 502: [pool www]
fpm_pctl_on_socket_accept() called"
-> It's not a big problem, because this doesn't take much time (in one
rare case it took ~90ms on my machine), but it's not nice, especially
when the server is flooded with requests
-> one idea:
- do not re-enable event-callback in fpm_pctl_on_socket_accept
- send an event from children just after accept() to parent process
- re-enable event-callback in parent process, when it receives this
event from children
- in case of an error it is re-enabled in the maintainance routine
after max 1s, which is IMHO not bad to throttle requests in case of
error
Stress tests
- Test-machine: Intel Core i7 930 (4 x 2.8 GHz) (VMware with 256 MB
RAM)
- Testing with 100 concurrent requests on the same pool to a sleep(10);
php script with 0 running processes and max_children = 200:
- took about 4ms per fork in average
- 25 processes are forked in one block (timeslice?), after this there
is a gap of 200-1000ms
- took about 125ms to fork 25 children
- took about 2.5s to fork all 100 children and accept the requests
- Testing with 200 concurrent requests
- hits RAM limit of VM, so it's maybe not meaningful
- took ~10.5s to fork all 200 children and accept the requests
- Testing with 10 concurrent requests on 20 pools (so in fact 200
concurrent requests)
- took ~11.2s to fork all 200 children and accept the requests
- all children are killed after process_timeout + 10s (1 process per
second per pool is killed) - OK
Previous Comments:
------------------------------------------------------------------------
[2010-08-30 10:18:14] mplomer at gmx dot de
Patch version 5:
- Added missing fpm_globals.is_child check (proposed by jerome)
- Implemented "max children reached" status counter.
- Fixed missing last_idle_child = NULL; in
fpm_pctl_perform_idle_server_maintenance which caused the routine to
shutdown only one (or a few?) processes per second globally instead per
pool, when you have multiple pools. I think this was not the intention,
and it's a bug.
------------------------------------------------------------------------
[2010-08-27 08:38:34] fat@php.net
Updates to come:
1- there is a bug. after fork, child process seems to run code reverved
to the
parent process:
Aug 27 08:32:30.646905 [WARNING] pid 4335, fpm_stdio_child_said(), line
143:
[pool www_chroot] child 4450 said into stderr: "Aug 27 08:32:30.628866
[DEBUG]
pid 4450, fpm_pctl_on_socket_accept(), line 529: [pool www_chroot] got
accept
without idle child available .... I forked, now=22184178.981102"
2- the 1s max delay before resetting the fpm_pctl_on_socket_accept() is
in
theory enough. But I prefer to set a much smaller specific timer (~1ms)
just in
case. Imagine there is a bug and children becomes to segfault and it's
not
restarted. There will be a 1s delay (max) before it's forked again. I
now it's
the worst case scenario.
------------------------------------------------------------------------
[2010-08-27 08:31:11] fat@php.net
here is a new revision:
1- I restore the backlog value check at startup. It's been simplified.
If it's
lower than 128, it's set to 128. I kept also the change of the backlog
default
value from -1 to 128. As the ondemand will certainely end up in trunk,
it's not
a violation of the 5.3 code.
2- you were right for the "else if (wp->config->pm ==
PM_STYLE_ONDEMAND)". I
thought there were a "if (wp->config->pm == PM_STYLE_STATIC)" on the
front of
the block
3- I change the libevent callback on pool listen_socket to prevent CPU
burns. If
max_childre is triggered, the callback function will be set up at next
process
maintenance call (every 1s).
------------------------------------------------------------------------
[2010-08-27 08:27:20] fat@php.net
The following patch has been added/updated:
Patch Name: fpm-ondemand.v4.patch
Revision: 1282890440
URL:
http://bugs.php.net/patch-display.php?bug=52569&patch=fpm-ondemand.v4.patch&revision=1282890440
------------------------------------------------------------------------
[2010-08-26 00:27:45] fat@php.net
For information, the listen.backlog default value has been changed from
-1 to
128 into trunk recentely: http://svn.php.net/viewvc?
view=revision&revision=302725
This changed won't be applied to 5.3 branch so as the ondemand process
manager
as it's a (big ?) new feature. It could be discussed.
I like the listen_backlog adjustment. It was maybe not perfect but
setting it to
0 will make the on demand PM not working.
for the "else if" fix, you have to add an "else {}" in all the cases. If
there
is a bug somewhere else, it's not advised to have a case which could not
be
checked.
it looks great. Can you also provides test results ?
thx a LOT for you help and your time making PHP better.
------------------------------------------------------------------------
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