RHEL 7.1-ksoftirqd thread reports high CPU utilization due to bug in ioatdma driver.

Issue

• The ksoftirqd thread/process reports high CPU utilization.
• top command shows high CPU usage from ksoftirqd thread without obvious reason.
• The Perf report shows that the tasklet_action is using most of the CPU when ioatdma module is in use.

$ perf report --stdio -k vmlinux
# To display the perf.data header info, please use --header/--header-only options.
#
# Samples: 119K of event 'cycles'
# Event count (approx.): 56534925982
#
# Overhead  Command      Shared Object      Symbol                                
# ........  ...........  .................  ......................................
#
    59.12%  ksoftirqd/2  [kernel.kallsyms]  [k] tasklet_action                    
    24.91%  ksoftirqd/2  [kernel.kallsyms]  [k] __do_softirq                      
     4.51%  ksoftirqd/2  [kernel.kallsyms]  [k] smpboot_thread_fn                 
     2.96%  ksoftirqd/2  [kernel.kallsyms]  [k] rcu_bh_qs                         
     2.40%  ksoftirqd/2  [kernel.kallsyms]  [k] __local_bh_enable                 
     1.93%  ksoftirqd/2  [kernel.kallsyms]  [k] __smp_mb__before_atomic           
     1.32%  ksoftirqd/2  [kernel.kallsyms]  [k] rcu_note_context_switch           
     1.01%  ksoftirqd/2  [kernel.kallsyms]  [k] run_ksoftirqd                     
     0.33%  ksoftirqd/2  [kernel.kallsyms]  [k] kthread_should_stop               
     0.32%  ksoftirqd/2  [kernel.kallsyms]  [k] kthread_should_park               
     0.31%  ksoftirqd/2  [kernel.kallsyms]  [k] msecs_to_jiffies                  
     0.31%  ksoftirqd/2  [kernel.kallsyms]  [k] _cond_resched