unrealircd 4.0.2: WARNING: Slow I/O engine or high load

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Callenbach
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unrealircd 4.0.2: WARNING: Slow I/O engine or high load

Post by Callenbach » Sat Mar 26, 2016 9:32 am

after we do a rehash than we get this txt msg *** WARNING: Slow I/O engine or high load: fd_select() took 1113 ms! read_callbacks=1, write_callbacks=0 can anyone tell me what this means we using unrealircd 4.0.2 thank you allready

Syzop
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Re: unrealircd 4.0.2

Post by Syzop » Mon Mar 28, 2016 10:36 am

What it means is that it took a long time (far too long) to process all events.
We added this notice so we would get notification if the I/O engine was too slow. However, the people who are seeing the notice nowadays are often experiencing a different issue: a slow machine.
I've seen this error on a shell with several ircds on it that had occasionally stalled briefly. I saw this even in an SSH session, if I did 'ls -al' it could freeze for several seconds, then continue. If such a case happens when UnrealIRCd is running, it will warn you about it.
Previous UnrealIRCd versions contained no such warnings, so possibly the same happened but you never noticed and you were never informed.

Are you on a shell shared with multiple users? How's the load average? How's the disk I/O speed? Several shell providers are quite horrible with regards to this, and even with the same shell provider there can be a difference between machine A and machine B.

If you get these multiple times a day something is definitely not good. If you only get them once or twice a week, I personally wouldn't worry too much, even though it's not a good indication (see above).

Oh yeah, you say it happens on /REHASH. On /REHASH quite some things will be done by UnrealIRCd, but it should never take 1100ms (1,1 second). Again, if that triggers this message, it too indicates the machine is too slow. Or are you running any special 3rd party modules that do a lot of things on (re)load?
The only other issue I can think of is if you are using remote includes (include http://....) and you are using cURL without c-ares support. We strictly recommend against this and during ./Config you should be warned about this if you try such a configuration, so that would be quite unlikely.

I'll see if we can get this message updated to be more descriptive, and some FAQ item.

Callenbach
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Re: unrealircd 4.0.2: WARNING: Slow I/O engine or high load

Post by Callenbach » Tue Mar 29, 2016 7:11 pm

Indeed in unreal32 I have never seen that message, as for my server is run fast ssh I can always good at work. But that message I get not too often so if that is what you have ween option attached how I'm certainly not pressure to make so often I see that message not. Thanks for the add for my question

ivp
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Re: unrealircd 4.0.2: WARNING: Slow I/O engine or high load

Post by ivp » Sat Sep 10, 2016 5:48 pm

After upgrade from 3.2 to 4.0.6 seeing plenty of "WARNING: Slow I/O engine or high load" messages.

Anybody have an idea what is the cause or how to find it?

Having dedicated server for IRC only. Load average: 0.69, 0.72, 0.67.

Code: Select all

[Fri Sep  9 18:31:38 2016] - WARNING: Slow I/O engine or high load: fd_select() took 2170 ms! read_callbacks=5, write_callbacks=0
[Fri Sep  9 18:43:25 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1205 ms! read_callbacks=2, write_callbacks=1
[Fri Sep  9 18:48:25 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1224 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 18:56:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1229 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:01:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1117 ms! read_callbacks=2, write_callbacks=1
[Fri Sep  9 19:06:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1217 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:07:19 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1255 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:07:22 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1187 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:07:36 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1676 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:07:39 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1321 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:13:25 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1435 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:16:31 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1063 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:18:25 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1181 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:31:39 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1328 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:36:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1036 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:38:25 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1369 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:51:02 2016] - WARNING: Slow I/O engine or high load: fd_select() took 2934 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:51:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1379 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 19:58:24 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1535 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 20:01:38 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1820 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 20:06:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1424 ms! read_callbacks=2, write_callbacks=1
[Fri Sep  9 20:11:27 2016] - WARNING: Slow I/O engine or high load: fd_select() took 2506 ms! read_callbacks=25, write_callbacks=0
[Fri Sep  9 20:11:31 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1258 ms! read_callbacks=2, write_callbacks=1
[Fri Sep  9 20:28:25 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1062 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 20:31:39 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1472 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 20:33:24 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1328 ms! read_callbacks=1, write_callbacks=0
[Fri Sep  9 20:36:32 2016] - WARNING: Slow I/O engine or high load: fd_select() took 1225 ms! read_callbacks=1, write_callbacks=0
'sar' command output:

Code: Select all

05:20:01 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
05:30:01 PM     all      0.83      0.00      0.45      1.30      0.00     97.42
05:40:01 PM     all      0.81      0.00      0.45      1.36      0.00     97.38
05:50:01 PM     all      0.72      0.00      0.42      1.21      0.00     97.65
06:00:01 PM     all      0.73      0.00      0.45      1.27      0.00     97.55
06:10:02 PM     all      0.80      0.11      0.49      1.49      0.00     97.11
06:20:01 PM     all      0.80      0.73      0.55      4.03      0.00     93.88
06:30:01 PM     all      0.78      0.00      0.49      1.20      0.00     97.53
06:40:01 PM     all      1.00      0.00      0.55      1.66      0.00     96.80
06:50:01 PM     all      1.16      0.00      0.61      1.18      0.00     97.06
07:00:01 PM     all      1.00      0.00      0.50      1.18      0.00     97.32
07:10:01 PM     all      1.08      0.80      0.58      4.92      0.00     92.61
07:20:01 PM     all      1.02      0.00      0.51      1.30      0.00     97.17
07:30:01 PM     all      0.95      0.00      0.47      1.33      0.00     97.25
07:40:01 PM     all      0.97      0.00      0.49      1.27      0.00     97.27
07:50:01 PM     all      0.93      0.00      0.50      1.36      0.00     97.21
08:00:01 PM     all      0.90      0.00      0.50      1.24      0.00     97.36
08:10:01 PM     all      0.95      0.11      0.54      1.63      0.00     96.78
08:20:01 PM     all      0.83      0.74      0.54      4.39      0.00     93.51
08:30:01 PM     all      0.82      0.00      0.50      1.25      0.00     97.42
Average:        all      0.78      0.18      0.46      1.81      0.00     96.77

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