Reducing latency on multicore pc's - Success!

Sure.

PC Hard disks are quite a bit slower than memory, and depending on the hardware involved in controlling them there may be a big burst of lag when you access them, like when any program starts.

Possible sources of delay include slow I/O hardware, disk controllers on the other side of a slow bus, a slow disk or a disk in a slow access mode (3 Gb instead of 6 Gb SATA, for instance) or even a failing hard disk that's generating errors.

You can test whether the disk is the problem by moving your program somewhere else to run it, like a RAMdisk if you have enough memory.

green751 wrote: Sure.

PC Hard disks are quite a bit slower than memory, and depending on the hardware involved in controlling them there may be a big burst of lag when you access them, like when any program starts.

Possible sources of delay include slow I/O hardware, disk controllers on the other side of a slow bus, a slow disk or a disk in a slow access mode (3 Gb instead of 6 Gb SATA, for instance) or even a failing hard disk that's generating errors.

You can test whether the disk is the problem by moving your program somewhere else to run it, like a RAMdisk if you have enough memory.

Thanks, will check that. Didn't thought hdd might be a "blocking function".
Happy new year!

What about Debian 7 with linuxcnc 2.6.1? I installed it from binary.hybrid.iso and same method doesn't work, still 8000ns to 10000ns
Ubuntu 10.04 works well: 1300ns to 4800ns

Hello

I am completely new to this.

I managed everything of this description except the grub modification:

The Max Jitters are down to 4764 (1ms) and 8522 (25ms).

I use the standard configuration of linux CNC including debian linux.

I added the following two lines to grub

isolcpus=1
acpi_irq_nobalance noirqbalance

I tried to call update-grub afterwards. I receive the error message that update-grub cannot be found.
therefore I called it directly:

sudo /usr/sbin/update-grub

the response is:

/usr/sbin/grub-mkonfig:35/etc/default/grub: acpi_irq_nobalance not found.

What do I do wrong?

Furthermore the provided debian version has no software center. How do i figure out if irqbalance is running?
best wishes

Doc Alex.

I tried Spainman's scripts on my machine and they seem to improve my latency.

My machine:
Club3D ATI Radeon X300 256MB PCI-E Silent
Gigabyte GA-P35-DS4 rev1.0
Intel Core2Duo E8400
4x1GB Ram
WD IDE HDD

BIOS settings:
All peripherals set to OFF, except LAN and LPT
Every setting that seems to alter the clock for power saving or performance: OFF

Kernel parameters copied from Spainman's first post in this thread:
"isolcpus=1 acpi_irq_nobalance noirqbalance"

In the attached picture, you can see
- latency-plot
- 3x gxlgears
- 1080p Big Buck Bunny

It seems like the upstart script provided by Spainman doesn't work with debian, so i called his set-irq-affinity script manually.
In the plot, i highlighted the point in time when i called "set-irq-affinity 1"
As you can see the latency spikes are reduced after this.



Edit:
It seems like i was a bit lucky taking this screenshot. It is true, that setting irq-affinity 1 calms down the small spikes, but sadly the huge spikes of ~17k are still happening, even with irq-affinity 1.

@Doc Alex:

I added the following two lines to grub

isolcpus=1
acpi_irq_nobalance noirqbalance

I think this has to be one line. you have to add it to the line you already have.
For example:
GRUB_CMDLINE_LINUX_DEFAULT="isolcpus=1 acpi_irq_nobalance noirqbalance lapic quiet rootdelay=5"

@qthree:
The reason might be, that the upstart script doesn't work on debian (at least it doesn't work on my machine)
I have no idea how this upstart stuff works, so i hope someone here can help us with this