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

[LeoY]

Hi Eric,

Thanks for your reply.
1. For the packet size, this idea is targeting some specific network card 
driver and we assume all the packet size will not exceed 2KB.
2. Currently only Uni-Processor is considered(Hyper-threading is also 
disabled), I will add spin lock part once it works on the UP.

Leo

----- Original Message ----- 
From: "Eric Dumazet" <dada1@xxxxxxxxxxxxx>
To: "LeoY" <multisyncfe991@xxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>; <netdev@xxxxxxxxxxxxxxx>
Sent: Saturday, October 08, 2005 3:09 PM
Subject: Re: Is this skb recycle buffer helpful to improve Linux network 
stack performance?


> LeoY a écrit :
> > 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;
> >  }
>
> Hum... Lot of problems I think
>
> Are you aware that skb_alloc() / skb_free() can handle data buffers of 
> different sizes ?
>
> So if you kmalloc() a small buffer, and store it later in your ring 
> buffer, you should not give it back to a caller that need a biger buffer.
>
> If you want your 'ring buffer'to work, I suspect you should ignore the 
> 'size' and let it be the max possible size handled in your machine.
>
> Then, dont forget about SMP and IRQs : I dont see in your code how you 
> protect against concurrent processors accessing your ring buffers, and how 
> you protect against IRQ (since a nic handler can runs on IRQ or softirq 
> context)
>
> kmalloc()/kfree() are SMP safe.
>
> > ----- Original Message ----- From: "Eric Dumazet" <dada1@xxxxxxxxxxxxx>
> > To: "LeoY" <multisyncfe991@xxxxxxxxxxx>
> > Cc: <netdev@xxxxxxxxxxxxxxx>
> > 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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