Description of problem:
I'm using RHEL 5 on a cluster environment for seismic simulation. In this enviroment we are using 32 HP's DL160 G6 powered with two Intel X5570 CPU using the new nehalem microarchitecture. In the default DL160 configuration, the OS sees 16 processors instead of 8 because of the hyperthreading
We saw a performance degradation when we moved from RHEL 5.4 to RHEL 5.5. Our simulations took 10% more time to run on the newer RHEL 5.5 using the same simulation software and dataset.
Version-Release number of selected component (if applicable):
kernel kernel-2.6.18-194.el5 and kernel-2.6.18-194.3.1.el5
Just start a simulation job with 8 parallel process and wait for simulation timing results gave after the simulation job finished. In RHEL 5.4's kernel version kernel-2.6.18-164.el5 we can see a steady result of ~856 secods with less then 1 percent of standard deviation. This RHEL 5.5's kernel version kernel-2.6.18-194.el5 or even with the newest errata kernel-2.6.18-194.3.1.el5 we can experiment a 10% increase in the processing time with more than 30% of standard deviation.
This are the times we can get with kernel-2.6.18-194.el5 and kernel-2.6.18-194.3.1.el5
Final cpu 987.82 elapsed 990.14
Final cpu 903.95 elapsed 906.42
Final cpu 999.24 elapsed 1001.67
Final cpu 898.51 elapsed 900.83
Final cpu 927.19 elapsed 929.51
This is the expected time and what we can get from kernel-2.6.18-164.el5
Final cpu 857.43 elapsed 859.96
Final cpu 856.02 elapsed 859.00
Final cpu 855.96 elapsed 858.78
Final cpu 856.09 elapsed 858.88
Final cpu 855.83 elapsed 858.81
We did an aditional test that involved installing RHEL 5.5 and downgrading just the kernel to kernel-2.6.18-164.el5 and the results are the same as running a full install RHEL 5.4, which means the expected result time of ~856 seconds.
It has been some time since this BZ was updated. Both customer issues have closed due to lack of updates. Closing NOTABUG.
If this is still an issue, please feel free to open a case with Red Hat Support via the Customer Portal.