对于DRR和WFQ一直比较混淆,想抽点时间搞清楚,发现里面还挺复杂的,基本上没有人能够说清楚.

DRR出自于http://www.ecs.umass.edu/ece/wolf/courses/ECE697J/papers/DRR.pdf

WFQ历史跟久远一些,实际上硬件很难实现它,一般实现的是MDRR(modified DRR)

下面是从这片paper里抽取的代码

 

//DC[i]:deficit counter,相当与token, 每一次round robin,都会update.

 

Initialization:

 for(i=0; i<n; i++)

     DC[i]=0;

 

Enqueue module: on arrival of packet p

i=ExtractFlow(p)

if(ExistsInActiveList(i) == FALSE) then

   InsertActiveList(i) //有packet了,把queue i加入active list

   DC[i]=0;

if no free buffers left then

   FreeBuffer()  //??什么意思呢

Enqueue(i,p);

 

Dequeue module:

  while(TRUE) do

      if ActiveList is not empty then

         Remove head of ActiveList, say flow i

         DC[i]=DC[i]+Q[i]    //Q[i]每一次round robin都会计算,根据bandwidth,weight,ActiveList

         while ((DC[i]>0) and (queue i not empty)) do

                    PacketSize=Size(Head(Queue i))

                    if(PacketSize <= DC[i]) then

                           Send(Dequeue(Queue i))

                           DC[i]=DC[i]- PacketSize

                    else  break                //尽可能的用完token;用不完的token带入下次round robin

                    if(Queue i empty) then

                            DC[i]=0     //为什么要清空呢?

                    Else

                            InsertActiveList(i)

 

这写代码还有不是很明白的地方.