Re: [PATCH][RFC 23/23]: Support for zero-copy TCP transmit of user space data

Evgeniy Polyakov
2008-12-23T21:38:35Z

On Tue, Dec 23, 2008 at 10:16:25PM +0300, Vladislav Bolkhovitin (vst@vlnb.net) wrote:
> Actually, there's another way, which seems to be a lot simpler. Alexey
> Kuznetsov privately suggested it to me.
>
> In skb_shared_info new pointer transaction_token would be added, which
> would point on:
>
> struct sk_transaction_token
> {
> atomic_t io_count;
> struct sk_transaction_token *next;
> unsigned long token;
> unsigned long private;
> void (*finish_callback)(struct
> sk_transaction_token *);
> };
>
> When skb is translated, transaction_token inherited. If 2 skb are merged
> (the same places where I put net_get_page's in my patch), the *older*
> token is inherited. This is the main point of this idea.
>
> Before starting new asynchronous send a client would open a new token.
> Everything sent then would receive that token. Finish_callback() would
> be called and the corresponding token freed, when io_count == 0 *AND*
> all previous tokens closed.
>
> This idea seems to be simpler, than even what Rusty implemented. Correct
> me, if I wrong. But, unfortunately, in the near future I will have no
> time to develop it.. :-(

Yes, it is simpler and cleaner, but it requires additional allocation.
This is additional (and quite noticeble) overhead.

--
Evgeniy Polyakov