Date: Tue, 13 Jun 2006 12:57:38 -0700 (PDT) From: Danial Thom <danial_thom@yahoo.com> To: Scott Long <scottl@samsco.org> Cc: freebsd-performance@freebsd.org, Robert Watson <rwatson@freebsd.org>, David Xu <davidxu@freebsd.org> Subject: Re: Initial 6.1 questions Message-ID: <20060613195738.64419.qmail@web33310.mail.mud.yahoo.com> In-Reply-To: <448F0C20.3090800@samsco.org>
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--- Scott Long <scottl@samsco.org> wrote:
> Danial Thom wrote:
> >
> > --- Robert Watson <rwatson@FreeBSD.org>
> wrote:
> >
> >
> >>On Tue, 13 Jun 2006, Danial Thom wrote:
> >>
> >>
> >>>Maybe someone can explain this output. The
> >>
> >>top line shows 99.6%idle. Is it
> >>
> >>>just showing CPU 0s stats on the top line?
> >>
> >>Two types of measurements are taken: sampled
> >>ticks regarding whether the
> >>system as a while is in {user, nice, system,
> >>intr, idle}, and then sampling
> >>for individual processes. Right now, the
> >>system measurements are kept in a
> >>simple array of tick counters called cp_time.
>
> >>John Baldwin and others have
> >>changes that make these tick counters
> per-CPU.
> >>The lines at the top of
> >>top(1)'s output are derived from those tick
> >>counters. Ticks are measured on
> >>each CPU, so those are a summary across all
> >>CPUs. To add cpustat support, we
> >>need to merge John's patch to make cp_time
> >>per-CPU (ie., different counters
> >>for different CPUs) and teach the userland
> >>tools to retrieve them. When you
> >>run top you'll notice that it adjusts the
> >>measurements each refresh. In
> >>effect, what it's doing is sampling the
> change
> >>in tick counts over the window,
> >>pulling down the new values and calculating
> the
> >>percentages of ticks in each
> >>"bucket" in the last window.
> >
> >
> > That doesn't explain why the Top line shows
> 99.6%
> > idle, but the cpu idle threads are showing
> > significant usage.
> >
> > I'm getting a constant 6000 Interrupts /
> Second
> > on my em controller, yet top jumps all over
> the
> > place; sitting at 99% idle for 10 seconds,
> then
> > jumping to 50%, then somewhere in between. It
> > seems completely unreliable. The load I'm
> > applying is constant.
> >
> > DT
>
> Be aware that there was a significant change
> made to if_em
> in 7-CURRENT in Jan 2006 to improve load
> performance. It'll
> probably get backported for 6.2, but you might
> consider
> looking at it before you make up your mind on
> 6.1 performance.
I can bridge 1 million pps with the em driver in
4.9, and it looks pretty much intact in 6.1, so
I'm not too worried about the em driver being the
problem here. Plus the measurements look just
fine with 1 cpu, and they are completely
impossible in SMP mode. So its reasonable to
conclude that the measurement tools simply don't
work.
Since everyone agrees that the load measuring
tools aren't all that accurate, what criteria was
used to determine that the changes made in 7 have
the effect that you think they have had?
DT
DT
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