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Re: code of process scheduling



sir!
  i am working on FC2 because this is the version available in my
institute.when i 've tried to study the sched.c
(/usr/src/linux-2.6.5-1.358/kernel/sched.c) , i came to know that same
MACRO name is used in so many different files. so , it was very hard
to understand that which file sched.c is using. I 've tried the  gcc -
E for getting the preprocessed file so that i may be able to locate
the files the sched is using. i 've found that by
compling/preprocessing thius file through gcc sched.c is n't able to
include mm.h,nmi.h etc. files.actually sched.c try to include the
files from /usr/include/linux directory not from
/usr/src/linux-2.6.5-1.358/include/linux where the files mm.h, nmi.h
etc. are available. i don't know which directory is actually used for
Kernel compilation . so; please give me some idea.
  one more thing i 've n't used  "make" utility to compile kernel.
i've used developer option during installation of FC2 . is it enough ?
as; i 'm gettingcompiled code in /usr/src/linux-2.6.5-1.358 directory.


Abhijit


On Thu, 7 Oct 2004 01:13:22 -0700, Nifty Hat Mitch
<mitch48 sbcglobal net> wrote:
> On Tue, Oct 05, 2004 at 12:51:12PM -0700, Nifty Hat Mitch wrote:
> > On Sat, Oct 02, 2004 at 08:11:28AM +0530, abhijit kumar wrote:
> > >
> > > dear programmers!
> > >   i am student pursuing a project on CORE fedora2. i want to change
> > > the sceduling algorithms used by the linux kernel and apply other
> ....
> 
> > I see that others have given you pointers to some files.
> > I suggest that you work on the current FC3 test version (FC3T2).
> > Developers will be more helpfull if you are forward looking.
> ...
> > What I am curious about are the goals of the project.
> 
>     Since abhijit and I swapped some off line mail on this school
>     project I suspect I should share my thoughts as they are of
>     general interest.
> 
> At one level this is a benchmarking project.
> Benchmarking  may be the single most important part!
> 
> First use Google search and collect some standard benchmark tools.  I
> would start with "lmbench".  These small benchmark tools are
> instrumented (have clock/ timer functions built in already.  Next
> build some benchmarks of your own design.  Hint, use exercises from
> previous classes.
> 
> Next in sched.c (/usr/src/linux-2.6.8-1.521/kernel/sched.c) play with
> the existing scheduler and see what changes. This does require that
> you recompile the kernel but does not require more or new code.  You
> can still break the system but the scope of change is more bounded.
> 
> Look for this code in kernel source.
>     /*
>      * These are the 'tuning knobs' of the scheduler:
>      *
>      * Minimum timeslice is 10 msecs, default timeslice is 100 msecs,
>      * maximum timeslice is 200 msecs. Timeslices get refilled after
>      * they expire.
>      */
>     #define MIN_TIMESLICE           ( 10 * HZ / 1000)
>     #define MAX_TIMESLICE           (200 * HZ / 1000)
>     #define ON_RUNQUEUE_WEIGHT       30
>     #define CHILD_PENALTY            95
>     #define PARENT_PENALTY          100
>     #define EXIT_WEIGHT               3
>     #define PRIO_BONUS_RATIO         25
>     #define MAX_BONUS               (MAX_USER_PRIO * PRIO_BONUS_RATIO / 100)
>     #define INTERACTIVE_DELTA         2
>     #define MAX_SLEEP_AVG           (AVG_TIMESLICE * MAX_BONUS)
>     #define STARVATION_LIMIT        (MAX_SLEEP_AVG)
> 
> The point in this step is the point is that a scheduler must balance
> various activities.  These kernel knobs control this balance as much
> or more than the algorithm.
> 
> There are also user space knobs....
> 
> As you work through the above you can look at scheduler code
> and make other specific changes based on what you discover
> in your baseline benchmarking and analysis.
> 
> Once the current scheduler has been parametrized you may understand
> which benchmarks are scheduler sensitive and why.
> 
> Some of the benchmark code you write should be selectively greedy for
> various system resources.
> 
> One obvious thing to watch for and measure is application startup
> time.  Here is the classic hello world (a.out).  Note that most timing
> tools are handy and require no special code.  Of interest the
> variability of run times is a result of scheduler actions.
> 
>     $ time a.out
>     Hello world
> 
>     real    0m0.004s
>     user    0m0.001s
>     sys     0m0.002s
>     $ time a.out
>     Hello world
> 
>     real    0m0.005s
>     user    0m0.000s
>     sys     0m0.003s
> 
> And simple "needs a window stuff" like this are fun...
> 
>     $ time xterm -e a.out
> 
>     real    0m0.305s
>     user    0m0.085s
>     sys     0m0.026s
> 
> Also for handy but non trivial benchmark stuff look at stuff like
> glxgears and x11perf.  There are also httpd and CGI benchmarks....
> 
> Do not ignore application profiling (strace, ltrace) and kernel profiling
> as benchmark tools.
> 
> Quiz for scheduler "want to be authors":
> 
> Given:
>        A two man racing team.
>        Race is 100 Km in length.
>        The first team member drives the first half at 50Km/hr.
> 
> Question 1:
>        How fast must the second driver drive the second
>        half of the race for the TEAM to average 100Km/hour?
> 
> Question 2:
>        Essay, How the heck does this apply to the Linux scheduler.
> 
> 
> 
> 
> --
>         T o m  M i t c h e l l
>         Me, I would "Rather" Not.
>


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