Performance issues after upgrade from SLES11 SP1 to SP2 or SP3

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Environment

SUSE Linux Enterprise Server 11 Service Pack 2

SUSE Linux Enterprise Server 11 Service Pack 3

Situation

An application is notably slower with SP2 compared to SP1. Tuning the dirty ratio of the virtual memory or disabling transparent hugepages (THP) doesn't improve the situation.

Same problem happens with SUSE Linux Enterprise Server 11 Service Pack 3.

Resolution

For SUSE Linux Enterprise Server 11 SP3, engineering fixed this issue with two updates of the packages Linux Kernel and cpupower. It's required to update at least to versions:

SUSE Linux Enterprise Server 11 SP3:
kernel-$FLAVOUR-3.0.101-0.15
cpupower-2.6.39-2.21

After updating to these package versions, available and used C-states can be shown with:

# cpupower idle-info

The desired C-State can be set with e.g.:

# cpupower idle-set -d 3

C-state no 3 gets disabled (not used by the kernel anymore) at runtime

# cpupower idle-set -e 3

will re-enable this state.

Two manpages have been added to the cpupower update as well which include more
detailed information:

cpupower-idle-info(1) and cpupower-idle-set(1)

Cause

On specific HW it may happen that a device is throwing interrupts with a frequency where the kernel thinks it makes sense to enter deeper CPU sleep states. Depending on this interrupt frequency and the CPU wakeup latency of the entered C-state, a decrease in IO performance can be seen.

Additional Information

SUSE Linux Enterprise Server 11 SP2:

Since SP2 is out of general support, no code fix is provided. Therefore the following boot/kernel parameter is a proper solution:

intel_idle.max_cstate=0

This might improve performance only when C-states for CPUs are disabled in the BIOS. If C states are enabled in the BIOS, you might still see performance issues. If that is the case, either disable them in the BIOS or additionally use the following kernel parameter:

processor.max_cstate=0

This disables C-states on kernel level.

Disclaimer

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