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Old 2008-12-19, 13:03   #1
S485122
 
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"Jacob"
Sep 2006
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Default Prime95 very slow after startup

Sometimes Prime95 is very slow (TF 20 times lower than usual, LL and P-1 times 2 to 4 slower...) Until now I had the problem only on 64 bits version. Most of the time rebooting the machine will help everything returning to normal. Recently a 32 bits machine had the problem as well and the 64 bits machine would not start normally despite a few reboots. The first time I had the problem was after completion of a P-1 job with Prime95 64 v24.14, but the problem is still there with Prime95 64 v25.8. I presume it is some memory contention problem (it is funny that TF will suffer as well), something like the memory requests being out of phase and "colliding" (not very scientific I know :-)

It is not a temperature problem, the affected machines will work according to specification most of the time.

Is there somebody else that experiences the same behaviour ?

Jacob
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Old 2008-12-19, 18:46   #2
cheesehead
 
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"Richard B. Woods"
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Quote:
Originally Posted by S485122 View Post
I presume it is some memory contention problem (it is funny that TF will suffer as well)
That TF has the same problem indicates that the contention is for timeslices, rather than memory.

Perhaps your system sometimes has some other task, of which you're unaware, using a significant fraction of cycles in those cases. (Perhaps a virus?)

Last fiddled with by cheesehead on 2008-12-19 at 18:48
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Old 2008-12-19, 23:09   #3
S485122
 
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"Jacob"
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It is a dedicated 64 bits system.

The machine is virus free. the fact that rebooting solves the condition most of the time is also incompatible with a virus.

No other tasks run as can be verified by looking at the total cpu time compared to the total time since boot. There are 16 tasks in all, one of them is "System Idle Process" and two of them are Prime95 : one v24.14 for P-1 factoring, one v25.8 on the three other cores for LL and TF.


The OS is Win XP 64 and that probably explains all :-(
I should move to Linux I suppose.

Jacob
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Old 2008-12-19, 23:26   #4
Uncwilly
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I have had a similar problem on an old machine at work.
http://www.mersenneforum.org/showthread.php?t=984
post # 16

The timing of reboot and log in seemed to have an effect. The machine drove me batty. Sometimes stopping Prime95 and restarting only seemed to slow things down. I don't think that I ever got it figured out. After a system crash and a newly imaged HD, I think that it got better.
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