Severe, irregular and unpredictable latency

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01 Jan 2010 16:39 - 01 Jan 2010 17:31 #1412 by lumberjack_jeff
I have an old compaq desktop running hardy and EMC 2.3.4

My machine misses steps because of severe occasional latency. Here's the last few lines of dmesg beginning at launch of emc and ending with the unexpected realtime delay error.
[424932.622097] I-pipe: Domain RTAI registered.
[424932.622121] RTAI[hal]: <3.6.1> mounted over IPIPE-NOTHREADS 2.0-04.
[424932.622125] RTAI[hal]: compiled with gcc version 4.2.4 (Ubuntu 4.2.4-1ubuntu3).
[424932.622134] RTAI[hal]: mounted (IPIPE-NOTHREADS, IMMEDIATE (INTERNAL IRQs DISPATCHED), ISOL_CPUS_MASK: 0).
[424932.622139] PIPELINE layers:
[424932.622142] dcc14000 9ac15d93 RTAI 200
[424932.622146] c0383180 0 Linux 100
[424932.654089] RTAI[malloc]: global heap size = 2097152 bytes, <BSD>.
[424932.655006] RTAI[sched]: loaded (IMMEDIATE, UP, USER/KERNEL SPACE: <with RTAI OWN KTASKs>, kstacks pool size = 524288 bytes.
[424932.655021] RTAI[sched]: hard timer type/freq = 8254-PIT/1193180(Hz); default timing: periodic; linear timed lists.
[424932.655027] RTAI[sched]: Linux timer freq = 250 (Hz), CPU freq = 1295673000 hz.
[424932.655032] RTAI[sched]: timer setup = 2010 ns, resched latency = 2688 ns.
[424932.791523] RTAI[math]: loaded.
[424933.082736] config string '0x378 out  '
[425244.799222] 320046: ERROR: Unexpected realtime delay: check dmesg for details.
[425244.799234] 
[425244.799235] In recent history there were
[425244.799237] 1262742, 1262027, 1261975, 1260451, and 1264032
[425244.799239] elapsed clocks between calls to the motion controller.
[425244.799245] This time, there were 17484805 which is so anomalously
[425244.799247] large that it probably signifies a problem with your
[425244.799250] realtime configuration.  For the rest of this run of
[425244.799252] EMC, this message will be suppressed.

Here is my lspci output
jeff@jeff-desktop:~$ lspci
00:00.0 Host bridge: Intel Corporation 82815 815 Chipset Host Bridge and Memory Controller Hub (rev 04)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 05)
00:1f.0 ISA bridge: Intel Corporation 82801BA ISA Bridge (LPC) (rev 05)
00:1f.1 IDE interface: Intel Corporation 82801BA IDE U100 Controller (rev 05)
00:1f.2 USB Controller: Intel Corporation 82801BA/BAM USB Controller #1 (rev 05)
00:1f.4 USB Controller: Intel Corporation 82801BA/BAM USB Controller #1 (rev 05)
02:0b.0 Multimedia audio controller: Aureal Semiconductor Vortex 2 (rev fa)
02:0d.0 Ethernet controller: Intel Corporation 82557/8/9/0/1 Ethernet Pro 100 (rev 0c)
02:0f.0 VGA compatible controller: S3 Inc. ViRGE/DX or /GX (rev 01)
jeff@jeff-desktop:~$
Last edit: 01 Jan 2010 17:31 by lumberjack_jeff. Reason: added info

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02 Jan 2010 02:14 #1413 by lumberjack_jeff
I may have partly resolved it... or at least figured out a workaround.

The computer is limited on processor power, and while running a program, system monitor indicated that my processor was pegged at 100% utilization for the duration of the program. This appears to be due to rendering of the toolpath in axis.

I did three things:
a) I switched to DRO view
b) I closed system monitor itself - the graph consumed fully half of my processor capacity (!) "htop" is a superior system monitoring tool.
c) I removed my sound card

I am trying to get the system to accept the S3virge video driver without any success as yet. Maybe this will improve things a bit more.

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02 Jan 2010 16:39 #1414 by lumberjack_jeff
Okay, I figured out a way to make it much worse... that's something, isn't it?

I was using the vesa video driver. I edited xorg.conf to use the "correct" S3virge driver and although cpu load dropped somewhat, latency went through the roof.

I also have a lot of horizontal line artifacts.

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