Message-ID: <4664CB6D.8060507@gmail.com>
Date:	Tue, 05 Jun 2007 10:33:17 +0800
From:	Li Yu <raise.sail@...il.com>
To:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] CFS scheduler, -v14


Ingo Molnar wrote:
> * Li Yu <raise.sail@...il.com> wrote:
>
>   
>> Also, I have want to know what's real meaning of
>>
>>    add_wait_runtime(rq, curr, delta_mine - delta_exec);
>>
>> in update_curr(), IMHO, it should be
>>
>>    add_wait_runtime(rq, curr, delta_mine - delta_fair);
>>
>> Is this just another heuristics? or my opinion is wrong again? :-)
>>     
>
> well, ->wait_runtime is in real time units. If a task executes 
> delta_exec time on the CPU, we deduct "-delta_exec" 1:1. But during that 
> time the task also got entitled to a bit more CPU time, that is 
> +delta_mine. The calculation above expresses this. I'm not sure what 
> sense '-delta_fair' would make - "delta_fair" is the amount of time a 
> nice-0 task would be entitled to - but this task might not be a nice-0 
> task. Furthermore, even for a nice-0 task why deduct -delta_fair - it 
> spent delta_exec on the CPU.
> 

Eh, I wrong again~ I even took an experiment in last week end, this idea 
is really bad! ;(

I think the most inner of source of my wrong again and again is
misunderstanding virtual time. For more better understanding this, I try 
to write one python script to simulate CFS behavior. However, It can not 
implement the fairness as I want. I really confuse here.

Would you like help me point out what's wrong in it? Any suggestion is 
welcome. Thanks in advanced.


#! /usr/bin/python

# htucfs.py - Hard-To-Understand-CFS.py ;)
# Wrote by Li Yu / 20070604

#
# only support static load on UP.
#


# Usage:
#    ./htucfs.py nr_clock_ticks_to_run
#

import sys

class task_struct:
    def __init__(self, name, load_weight):
        self.name = name
        self.wait_runtime = 0
        self.fair_clock = 0
        self.fair_key = 0
        self.load_weight = float(load_weight)
    def __repr__(self):
        return "%s/C%.2f" % (self.name, self.fair_clock)

idle_task = task_struct("idle", 0)

class run_queue:
    def __init__(self):
        self.raw_weighted_load = 0
        self.wall_clock = 0
        self.fair_clock = 0
        self.ready_queue = {}
        self.run_history = []
        self.task_list = []
        self.curr = None
        self.debug = 0

    def snapshot(self):
        if self.debug:
            print "%.2f" % self.fair_clock, self.ready_queue, self.curr

    def enqueue(self, task):
        task.fair_key = self.fair_clock-task.wait_runtime
        task.fair_key = int(100 * task.fair_key)
        if not self.ready_queue.get(task.fair_key):
            self.ready_queue[task.fair_key] = [task]
        else:
            # keep FIFO for same fair_key tasks.
            self.ready_queue[task.fair_key].append(task)
        self.raw_weighted_load += task.load_weight
        self.task_list.append(task)

    def dequeue(self, task):
        self.raw_weighted_load -= task.load_weight
        self.ready_queue[task.fair_key].remove(task)
        if not self.ready_queue[task.fair_key]:
            del self.ready_queue[task.fair_key]
        self.task_list.remove(task)

    def other_wait_runtime(self):
        for task in self.task_list:
            self.dequeue(task)
            task.wait_runtime += 1
            self.enqueue(task)

    def clock_tick(self):
        # clock_tick = 1.0
        self.fair_clock += 1.0/self.raw_weighted_load
        # delta_exec = 1.0
        delta_mine = self.curr.load_weight / self.raw_weighted_load
        self.curr.wait_runtime += (delta_mine-1.0)
        self.curr.fair_clock += 1.0/self.curr.load_weight
        self.dequeue(self.curr)
        self.other_wait_runtime()
        self.enqueue(self.curr)
        self.pick_next_task()

    def pick_next_task(self):
        key_seq = self.ready_queue.keys()
        if key_seq:
            key_seq.sort()
            self.curr = self.ready_queue[key_seq[0]][0]
        else:
            self.curr = idle_task
        self.snapshot()
        self.record_run_history()

    def record_run_history(self):
        task = self.curr
        if not self.run_history:
            self.run_history.append([task, 1])
            return
        curr = self.run_history[-1]
        if curr[0] != task:
            self.run_history.append([task, 1])
        else:
            curr[1] += 1

    def show_history(self):
        stat = {}
        for entry in self.run_history:
            task = entry[0]
            nsec = entry[1]
            print "%s run %d sec" % (task, nsec)
            if task not in stat.keys():
                stat[task] = nsec
            else:
                stat[task] += nsec
        print "=============================="
        tasks = stat.keys()
        tasks.sort()
        for task in tasks:
            print task, "/", task.load_weight, ":", stat[task], "sec"
        print "=============================="

    def run(self, delta=0, debug=0):
        self.debug = debug
        until = self.wall_clock + delta
        print "-----------------------------"
        self.pick_next_task()
        while self.wall_clock < until:
            self.wall_clock += 1
            self.clock_tick()
        print "-----------------------------"

#
# To turn this, display verbose runtime information.
#
debug = True

if __name__ == "__main__":
    rq = run_queue()
    task1 = task_struct("TASK_1", 1)
    task2 = task_struct("TASK_2", 1)
    task3 = task_struct("TASK_3", 2)
    rq.enqueue(task1)
    rq.enqueue(task2)
    rq.enqueue(task3)
    rq.run(int(sys.argv[1]), debug)
    rq.show_history()

#EOF

Good luck

- Li Yu
-
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