Many mfgpt timer interrupts with tickless kernel
olpc-devel at kernel.dk
Thu Mar 22 13:26:50 EDT 2007
On Thu, Mar 22 2007, William Cohen wrote:
> Hi all,
> I was trying to make sense of the data that I collected earlier with the
> idle1.stp probe. It displayed the percentage of time spent in halted mode,
> which the highest I saw on an idle machine was 17 percentage. This seemed
> rather low for a machine that was doing nothing, so I took a closer look at
> what was going on the idle machine. All this work is based on kernel built
> from dilinger's:
> I ran an experiment where the machine state idle for 10 seconds with the
> systemtap script running. I also compared the number of interrupts before
> and after the experiment. There is about 150 interrupts per second from the
> mfgpt timer. I thought with the tickless kernel that this would be a lot
> Below is the data from the experiment. I tried booting the machine in
> runlevel three and got the same results, about 150 interrupts per second.
> Why so many timer interrupts for tickless kernel?
The tickless kernel just _enables_ low number of interrupts per second,
it'll still wakeup everytime something is scheduled to run. So you
probably want to look into _why_ th timer interrupts happen so often -
who is the user of them?
I see ~70 interrupts/sec here with an idle machine in X, FWIW.
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