Process scheduling

[Nitin Varyani]

thanks

On Sat, Feb 13, 2016 at 2:19 PM, Henrik Austad <henrik at austad.us> wrote:

> On Sat, Feb 13, 2016 at 11:42:57AM +0530, Nitin Varyani wrote:
> > Hello,
>
> Hi Nitin,
>
> >          I want to understand the flow of code of process scheduler of
> > linux kernel. What I have understood is that
> > The task marks itself as sleeping,
> > puts itself on a wait queue,
> > removes itself from the red-black tree of runnable, and
> > calls schedule() to select a new process to execute.
> >
> > for Waking back up
> > The task is set as runnable,
> > removed from the wait queue,
> > and added back to the red-black tree.
> >
> > Can I get the details of which function does what? in sched/core.c and in
> > sched/fair.c
> > I am concerned only with fair scheduler. There are so many functions in
> > these two files that I am totally confused.
>
> Then core.c and fair.c is the best bet.
>
> You could also pick up a copy of Linux kernel development (By Love), it
> gives a nice introduction to the overall flow of .. well mostly everything.
> :)
>
> In kernel/sched/sched.h you have a struct called 'struct sched_class" which
> is a set of function-points. This is used by the core machinery to call
> into scheduling-class specific code. At the bottom of fair.c, you see said
> struct being populated.
>
> Also, if you want to see what really happens, try enabling
> function-tracing, but limit it to sched-functions only (and sched-events,
> those are also useful to see what triggers things)
>
> mount -t debugfs nodev /sys/kernel/debug
> cd /sys/kernel/debug/tracing
> echo 0 > tracing_on
> echo function > current_tracer
> echo "sched*" > set_ftrace_filter
> echo 1 > events/sched/enable
> echo 1 > tracing_on
> ... wait for a few secs
> echo 0 > tracing_on
>
> cat trace > /tmp/trace.txt
>
> Now, look at trace.txt and correlate it to the scheduler code :)
>
> Good luck!
>
> --
> Henrik Austad
>
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