Re: [uml-devel] Dramatic drop in C3 state residency with NO_HZ patches

[Hrishikesh <hri...@gm...>]

Hey Jeff,
Yes, that double negative was a slipup. I did get some numbers out and they
look pretty good. I ran upto 5 instances of UML simultaneously and in the
tickful case, each instance adds roughly about 100 wakeups per second. So
after 5 instances, C3 residency comes down to about 95% when all the
instances are simply idling. With NO_HZ applied, the change is minimal with
C3 residency still approximately 98%. UML is not even among the top three of
the bad-list of wakers-up :-)
Hrishikesh

On 10/18/07, Jeff Dike <jd...@ad...> wrote:
>
> On Wed, Oct 17, 2007 at 07:29:47PM -0400, Hrishikesh wrote:
> > No, I think I haven't been clear enough. The story is right :-) When it
> is
> > "busy-looping" like in the second case is when the C3 residency comes
> down,
> > as expected. Like you said, it looks broken, and has to be fixed.
>
> Yes, your original post was a bit confusing:
>
> > This happens when you run a
> > patched kernel but without the NO_HZ and HR timers options disabled.
>
> To my highly logical mind, that double-negative says that you saw the
> C3 drop with NO_HZ and hrtimers enabled.
>
> There was also this, which I paid insufficient attention to:
>
> > This does not happen when the tickless option _is_ enabled.
>
> However, it does look like the tickless support induces UML into a
> busy loop when NO_HZ is disabled.
>
> BTW, can you measure C3 time with a before-NO_HZ UML, so we can see
> that NO_HZ has some sort of benefit on power consumption?
>
>                                 Jeff
>
> --
> Work email - jdike at linux dot intel dot com
>