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cmay4
Tux's lil' helper
Joined: 18 May 2002
Posts: 109
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 Posted: Mon Mar 31, 2003 9:12 pm Post subject: seti@home and nice |
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I thought that if something was niced to 19, then it would essentially idle if other things were using the cpu. This doesn't seem to be the case. Look at the top output:
| Code: |
PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
26633 may 18 0 56156 54M 4048 R 84.3 21.9 0:37 cc1plus
24802 root 19 19 14836 14M 788 R N 13.7 5.7 75:50 setiathome
26618 may 10 0 1152 1152 824 R 1.9 0.4 0:00 top
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Normally the cc1plus gets just about all of the cycles (> 98%). Shouldn't setiathome be close to 0%?
Is this just my misunderstanding of nice? |
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sputnik1969
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Joined: 08 Aug 2002
Posts: 401
Location: Berlin / Germany
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| Posted: Tue Apr 01, 2003 12:02 am Post subject: |
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cc1plus CAN'T use all cycles, because it has sometime to wait for fileoperations and similar. In this moment the scheduler switches to setiathome and it's getting "his" part of the CPU for a while.
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cmay4
Tux's lil' helper
Joined: 18 May 2002
Posts: 109
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| Posted: Tue Apr 01, 2003 2:32 am Post subject: |
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| sputnik1969 wrote: | | cc1plus CAN'T use all cycles, because it has sometime to wait for fileoperations and similar. In this moment the scheduler switches to setiathome and it's getting "his" part of the CPU for a while. |
How about this Python script:
| Code: | #!/usr/bin/env python
while 1:
pass |
which produces the same results:
| Code: | PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
925 may 16 0 2144 2144 1576 R 84.1 0.8 1:16 python
24802 root 19 19 15864 15M 788 R N 13.8 6.1 389:38 setiathome
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It seems to me that that script should definitely get 100% of the CPU. |
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sputnik1969
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Joined: 08 Aug 2002
Posts: 401
Location: Berlin / Germany
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| Posted: Tue Apr 01, 2003 3:29 am Post subject: |
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| cmay4 wrote: | | sputnik1969 wrote: | | cc1plus CAN'T use all cycles, because it has sometime to wait for fileoperations and similar. In this moment the scheduler switches to setiathome and it's getting "his" part of the CPU for a while. |
How about this Python script:
| Code: | #!/usr/bin/env python
while 1:
pass |
which produces the same results:
| Code: | PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
925 may 16 0 2144 2144 1576 R 84.1 0.8 1:16 python
24802 root 19 19 15864 15M 788 R N 13.8 6.1 389:38 setiathome
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It seems to me that that script should definitely get 100% of the CPU. |
No, it should NOT!
Linux-process-scheduling is based on Round-Robin and gives every process at every turnaround at least one timeslot (Priority 19), two slots with Prio 18, three with prio 17... and so on...
the process gets it's slot as long as he a) don't uses a kernelroutine which causes the process to wait or b) the schedules interrupts it cause it's time(slot) ends.
Try to run your Python-Script with Prio -10 and see what happens 
The Setiathome-process uses much less io then "normal" processes, so it will get more CPU then other processes with the same priority.
My opinion is, that the linux-schedule has to be tunend in future, to get "finer" granulation between the processes  (Not 19 to -20 but -128 to 127 like in good old AMigaOS-Times)
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'Cynic' is a word invented by optimists to criticize realists. - Nigel. In the ocean of Night by Gregory Benford
"Zyniker" ist ein Wort das Optimisten erfunden haben um Realisten zu kritisieren. - Nigel. Im Meer der Nacht von Gregory Benford |
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cmay4
Tux's lil' helper
Joined: 18 May 2002
Posts: 109
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| Posted: Tue Apr 01, 2003 4:12 am Post subject: |
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I'm sure it was my misunderstanding. I was just under the impression that something with that nice value would not (or at least barely) affect other running software. I made a slight modification:
| Code: | #!/usr/bin/env python
for i in range(0,100000000):
pass |
And timed it with and without seti@home running.
Without seti@home: 57.348 secs
With seti@home: 60.186 secs
Roughly a 5% difference; not a big deal. If in general we are talking about 5%, then it's not that big a deal.
I'm going to try kernel compiles next... |
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sputnik1969
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Joined: 08 Aug 2002
Posts: 401
Location: Berlin / Germany
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| Posted: Tue Apr 01, 2003 4:46 am Post subject: |
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| cmay4 wrote: |
Without seti@home: 57.348 secs
With seti@home: 60.186 secs
Roughly a 5% difference; not a big deal. If in general we are talking about 5%, then it's not that big a deal.
I'm going to try kernel compiles next... |
I never tested things like this, the only thing i know is, that i kill seti if i plan to play a 3d-shooter or similar, because you see the difference (small drops in performance are "viewable" )
In all other cases, i think a "loss" of cpupower up to 10% is tolerable with my XP1900
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'Cynic' is a word invented by optimists to criticize realists. - Nigel. In the ocean of Night by Gregory Benford
"Zyniker" ist ein Wort das Optimisten erfunden haben um Realisten zu kritisieren. - Nigel. Im Meer der Nacht von Gregory Benford |
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cmay4
Tux's lil' helper
Joined: 18 May 2002
Posts: 109
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| Posted: Tue Apr 01, 2003 4:50 am Post subject: |
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Kernel compile numbers:
With seti@home: 13min 30sec
Without seri@home: 11min 32sec
Or 14.5% slower with seti@home. 5% is one thing, but that is too much.
Doesn't that seem to be too large a difference? |
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nempo
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Joined: 16 Apr 2002
Posts: 360
Location: Linkoping, Sweden
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| Posted: Tue Apr 01, 2003 2:18 pm Post subject: |
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Everytime I've had seti@home running I've been unable to run any kind of opengl software, why? well every 2s or so the rendering stops for ½s and then continues, this constantly happens. Seti@home was running at 19 while the opengl ran at the default 0.
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sputnik1969
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| Posted: Tue Apr 01, 2003 2:46 pm Post subject: |
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Everything here are based upon the same problem:
Linux doesn't know "true" idle-processes and the priority-system isn't "fine" enough...
Multiprocessing under Linux works with "timeslices" / slots.
If there are 2 processes running with different priorities (e.g. process Seti Prio 19 and Q3A Prio 0) both processes share the slots, seti gets at least minimal 1 slot of 20 (difference between priority of Seti and Q3A) and Q3A gets the rest... But this single timeslice has the effect, that 1/20 (5%) of the time quake has to wait for seti, even if seti should be idle 
If priority-system would range from -128 to 127 (like Amiga-OS) and Seti would run with 127 and Q3A with 0, it would get at least 1/128 (<1%)
But then timeslices have to be shorter, or latency will be a really big problem
Also this needs more cputime for the scheduler
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'Cynic' is a word invented by optimists to criticize realists. - Nigel. In the ocean of Night by Gregory Benford
"Zyniker" ist ein Wort das Optimisten erfunden haben um Realisten zu kritisieren. - Nigel. Im Meer der Nacht von Gregory Benford |
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cmay4
Tux's lil' helper
Joined: 18 May 2002
Posts: 109
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| Posted: Tue Apr 01, 2003 4:58 pm Post subject: |
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Thanks for the input. I appreciate your help.
I have one question though. I've read about the new scheduler in the 2.5 kernel. Would it make any difference in this situation? |
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zephyr1256
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Joined: 10 Mar 2003
Posts: 170
Location: Kingsport, TN
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| Posted: Tue Apr 01, 2003 8:01 pm Post subject: |
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I have to turn Seti off for opengl apps and for one other case(that I've found so far), whenever I use openoffice.org, seti has to be turned off. Often OO won't even display if I switch to the screen that has it if seti is running.  Nice levels don't help with this, I always use 19, but Seti, unlike most other programs is highly CPU bound. I guess some programs often do system calls but they depend on getting the CPU again sooner than they do with Seti running. Programs like that need to have Seti shut down(or relegated to another processor if you are fortunate to have a MP machine). |
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sputnik1969
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Joined: 08 Aug 2002
Posts: 401
Location: Berlin / Germany
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| Posted: Fri Apr 04, 2003 2:41 am Post subject: |
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| zephyr1256 wrote: | | I have to turn Seti off for opengl apps and for one other case(that I've found so far), whenever I use openoffice.org, seti has to be turned off. Often OO won't even display if I switch to the screen that has it if seti is running. |
Sorry, Dude, I don't know what kind of machine you are running, but my AthlonXP1900+/512MB SD-133 has got no problem with seti and oo...
Sometime oo needs a little more time to update it's display, but i can live with it Also mplayer creates high cpuload with hires-videos (with high postprocessing settings) and i don't habe seen any problems yet.
_________________
'Cynic' is a word invented by optimists to criticize realists. - Nigel. In the ocean of Night by Gregory Benford
"Zyniker" ist ein Wort das Optimisten erfunden haben um Realisten zu kritisieren. - Nigel. Im Meer der Nacht von Gregory Benford |
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sputnik1969
Guru
Joined: 08 Aug 2002
Posts: 401
Location: Berlin / Germany
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| Posted: Fri Apr 04, 2003 2:53 am Post subject: |
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| cmay4 wrote: | Thanks for the input. I appreciate your help.
I have one question though. I've read about the new scheduler in the 2.5 kernel. Would it make any difference in this situation? |
I haven't testet the new scheduler and shame on me, i didn't inform myself about internels of the new scheduler yet. but i will do soon...
_________________
'Cynic' is a word invented by optimists to criticize realists. - Nigel. In the ocean of Night by Gregory Benford
"Zyniker" ist ein Wort das Optimisten erfunden haben um Realisten zu kritisieren. - Nigel. Im Meer der Nacht von Gregory Benford |
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