Re: Is this skb recycle buffer helpful to improve Linux network stack performance?

["LeoY" <multisyncfe991@hotmail.com>]

Here is the modifications I made:
//skbuff.h
//I added the folloing definitions
#define MAX_POOL_SIZE 4096
unsigned char *skbuff_data_pool[MAX_POOL_SIZE];
int skbPoolHead, skbPoolTail;


//skb_init()
//I add the following codes:
for(i=0;i<MAX_POOL_SIZE;i++)
        skbuff_data_pool[i] = NULL;
skbPoolHead = skbPoolTail = 0;


//alloc_skb()
//I made the following changes
if (skbuff_data_pool[skbPoolHead])
{
  data = skbuff_data_pool[skbPoolHead];
 skbuff_data_pool[skbPoolHead] = NULL;
 if (++skbPoolHead == MAX_POOL_SIZE)
  skbPoolHead = 0;
}
else{ //Original path
 size = SKB_DATA_ALIGN(size);
 data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
 }

//skb_release_data()
//I made the following changes:
 if ((skbPoolHead == skbPoolTail) && (skbuff_data_pool[skbPoolHead] != 
NULL))
 //Original path
  kfree(skb->head);
               else{
  if (skbuff_data_pool[skbPoolTail])
   panic("Tail pointer must be null");

  skbuff_data_pool[skbPoolTail] = skb->head;
                       if (++skbPoolTail == MAX_POOL_SIZE)
   skbPoolTail = 0;
 }

----- Original Message ----- 
From: "Eric Dumazet" <dada1@cosmosbay.com>
To: "LeoY" <multisyncfe991@hotmail.com>
Cc: <netdev@vger.kernel.org>
Sent: Saturday, October 08, 2005 2:47 PM
Subject: Re: Is this skb recycle buffer helpful to improve Linux network 
stack performance?


> LeoY a écrit :
> > Hi,
> >
> > Motivation: we noticed alloc_skb()/kfree() used lots of clock ticks when
> > handling heavy network traffic. As Linux kernel always need to call
> > kmalloc()/kfree() to allocate and deallocate a skb DATA buffer(not 
> > sk_buff)
> > for each incoming/outgoing packet, we try to reduce the frequence of 
> > calling
> > these memory functions.
> >
> > I wangt to set up a ring buffer in Linux kernel(skbuff.c) and recycle 
> > those
> > skb data buffers. The basic idea is as follows:
> > 1. Create a ring buffer. This ring buffer has a head pointer which points 
> > to
> > the virtual address of the data buffer to be reused; It also has a tail
> > pointer, which can be used to store the virutal address of skb data 
> > buffer
> > for those transmitted packets.
> > 2. If the ring buffer is full, just use normal kmalloc()/kfree() 
> > operation
> > to manager those skb data buffers instead of recycling them.
> > 3. if any DATA buffer is available, Instead of calling kmalloc(), assign 
> > a
> > skb data buffer directly from ring buffer to the incoming packets.
> > 4. If ring buffer still has space, Instead of calling kfree(), store the 
> > skb
> > data buffer into the ring buffer.
> > 5. if the head and tail pointer overlap and head pointer is not empty, 
> > just
> > stop accpeting more DATA buffer until some DATA buffer is used for the
> > incoming packets.
> >
> > I tested my method on the latest Linux kernel 2.6.13.3, it works with the
> > normal traffic; However, the Linux kernel crashed under the heavy network
> > traffic.
> >
> > Any idea to make this ring bufer work under the heavy network traffic?
>
> Your idea seems interesting, but you forgot to post a link to the code you 
> wrote. How do you want us to help you ?
>
> Eric
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