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

Vladislav Bolkhovitin
2008-12-24T14:41:49Z

Evgeniy Polyakov, on 12/24/2008 12:38 AM wrote:
> 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.

Not necessary requires. For instance, in iscsi-scst sk_transaction_token
can (and should) be part of iSCSI cmd structure, so no additional
allocations would be needed.

Thanks,
Vlad