I have dual core E5440 based HP DL380 server installed with Linux Ubuntu 18.104.22.168.
The SMP is enabled with few of the CPU cores isolated for dedicated applications.
The Kernel is booted with cpuisol command as
Kernel command line: BOOT_IMAGE=/vmlinuz-2.6.31 root=/dev/mapper/mylinux-root ro isolcpus=1,2,3,4,5,6 noapictimer crashkernel=384M-2G:64M,2G-:128M quiet splash
I run the test application on the isolated core through CPU affinity settings. What I have observed is that I do not get consistant execution time for
the test application. Out of 10K runs, there are always some outliers 10-20 that push the execution time higher by as much as 500usecs.
Obviously, the processor isolation is not 100% working. I have tried to isolate interrupts to other cores but that did not help.
If I repeat the exact same experiment with same Kernel version on AMP Opteron machine, I get very clean and predicatble results with
no outliers. I am wondering if the combination of multi-core XEON and SMP is the cause of the problem where unwanted L2 cache invalidations
are causing outlier spikes.
Appreciate ideas, the objective is to have full 100% user control on a cou core with no disruption from OS and interrupts.
When I install and run the Kernel on AMD based 8 Core machine