Messages in this thread | | | Date | Sun, 09 Oct 2005 00:09:57 +0200 | From | Eric Dumazet <> | Subject | Re: Is this skb recycle buffer helpful to improve Linux network stack performance? |
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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@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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