09-30-2008
I/O may cause a process to lose current context. ie. switch context.
What I/O scheduler are you using: AS, CFQ?
If your %iowait is high try increasing quantum.
It is possible to see 100% iowait. What iowait really measures is the percent of time at least one process is in an iowait state. I would bet your system shows a high values during the context switch rush.
cfq is able to dedicate a time slice to each process that uses a block device. You can adjust the time slice. Consider looking into that.
Since you are not incurring a cpu hit, all you are doing is increasing wasted cpu time in context switches. Rather than something more useful. IMO.
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LEARN ABOUT CENTOS
tapset::scheduler
tapset::scheduler(3stap) tapset::scheduler(3stap)
NAME
tapset::scheduler - systemtap scheduler tapset
DESCRIPTION
scheduler.cpu_off
Process is about to stop running on a cpu
See probe::scheduler.cpu_off(3stap)
for details.
scheduler.cpu_on
Process is beginning execution on a cpu
See probe::scheduler.cpu_on(3stap)
for details.
scheduler.tick
Schedulers internal tick, a processes timeslice accounting is updated
See probe::scheduler.tick(3stap)
for details.
scheduler.balance
A cpu attempting to find more work.
See probe::scheduler.balance(3stap)
for details.
scheduler.ctxswitch
A context switch is occuring.
See probe::scheduler.ctxswitch(3stap)
for details.
scheduler.kthread_stop
A thread created by kthread_create is being stopped
See probe::scheduler.kthread_stop(3stap)
for details.
scheduler.kthread_stop.return
A kthread is stopped and gets the return value
See probe::scheduler.kthread_stop.return(3stap)
for details.
scheduler.wait_task
Waiting on a task to unschedule (become inactive)
See probe::scheduler.wait_task(3stap)
for details.
scheduler.wakeup
Task is woken up
See probe::scheduler.wakeup(3stap)
for details.
scheduler.wakeup_new
Newly created task is woken up for the first time
See probe::scheduler.wakeup_new(3stap)
for details.
scheduler.migrate
Task migrating across cpus
See probe::scheduler.migrate(3stap)
for details.
scheduler.process_free
Scheduler freeing a data structure for a process
See probe::scheduler.process_free(3stap)
for details.
scheduler.process_exit
Process exiting
See probe::scheduler.process_exit(3stap)
for details.
scheduler.process_wait
Scheduler starting to wait on a process
See probe::scheduler.process_wait(3stap)
for details.
scheduler.process_fork
Process forked
See probe::scheduler.process_fork(3stap)
for details.
scheduler.signal_send
Sending a signal
See probe::scheduler.signal_send(3stap)
for details.
SEE ALSO
probe::scheduler.cpu_off(3stap), probe::scheduler.cpu_on(3stap), probe::scheduler.tick(3stap), probe::scheduler.balance(3stap),
probe::scheduler.ctxswitch(3stap), probe::scheduler.kthread_stop(3stap), probe::scheduler.kthread_stop.return(3stap),
probe::scheduler.wait_task(3stap), probe::scheduler.wakeup(3stap), probe::scheduler.wakeup_new(3stap), probe::scheduler.migrate(3stap),
probe::scheduler.process_free(3stap), probe::scheduler.process_exit(3stap), probe::scheduler.process_wait(3stap),
probe::scheduler.process_fork(3stap), probe::scheduler.signal_send(3stap), stap(1), stapprobes(3stap)
IBM
--- tapset::scheduler(3stap)