Why we see higher CPU usage with RHEL 6 as compared to RHEL 5 systems?
Issue
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Recently migrated a multi-threaded application to RHEL 6.3 from RHEL 5.7. Although the code base is the same and no changes have gone in during the migration, the application seemed to be using higher CPU cycles (observed using 'top') with 6.3 version of the OS. Even an application in idle state takes extra CPU cycles.
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For example, wrote a simple test application with a block on "select call" with a timed wait of 1 ms which was taking 0% CPU on 5.7, currently takes around 0.7 to 1% CPU on RHEL 6.3. 'perf report' of the sample test application is as follows :
55.62% a.out [kernel.kallsyms] [k] find_busiest_group
18.17% a.out [kernel.kallsyms] [k] _spin_lock
7.81% a.out [kernel.kallsyms] [k] update_curr
5.86% a.out [kernel.kallsyms] [k] dequeue_entity
5.57% a.out [kernel.kallsyms] [k] core_sys_select
3.92% a.out [kernel.kallsyms] [k] thread_return
2.66% a.out [kernel.kallsyms] [k] mpage_alloc
0.28% a.out [kernel.kallsyms] [k] copy_user_generic_string
0.05% a.out [kernel.kallsyms] [k] perf_pmu_rotate_start
0.03% a.out [kernel.kallsyms] [k] native_write_msr_safe
Environment
- Red Hat Enterprise Linux 6
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