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SubjectRe: [RFC PATCH RT] rwsem: The return of multi-reader PI rwsems
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On Thu, 2014-04-10 at 23:25 -0400, Steven Rostedt wrote: 
> On Fri, 11 Apr 2014 04:50:26 +0200
> Mike Galbraith <umgwanakikbuti@gmail.com> wrote:
>
> > Oh, there was another useful bit.
> >
> > 3.12.17-rt25 403991 384216 377786
> > 405466 394011 392850
> >
> > 3.12.17-nopreempt 109049 186133 118766 !?!.. ew, TTWU_QUEUE
> > 350385 318786 367336 !TTWU_QUEUE
> > 326009 356939 378215 !TTWU_QUEUE
> >
> > IPI == low-pass filter.
>
> I'm sorry, but I don't have the foggiest clue to what the above means.

It means..

# Overhead Symbol
# ........ .......................................................................................................................................................................................
#
17.33% [k] native_write_msr_safe
|
|--88.45%-- __x2apic_send_IPI_mask
| |
| |--97.89%-- try_to_wake_up
| | |
| | |--99.91%-- wake_futex
| | | |
| | | |--99.77%-- futex_wake_op
| | | | do_futex
| | | | sys_futex
| | | | system_call_fastpath

..wakeup frequency is restricted by the IPI.

-Mike



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