Zerocopy networking patch, 2.4.0-1
Quoted 6 lines · sct
We've already got measurements showing how insane this is. Raw IO requests, plus internal pagebuf contiguous requests from XFS, have to get broken down into page-sized chunks by the current
ll_rw_block()API, only to get reassembled by themake_requestcode. It's *enormous* overhead, and the kiobuf-based disk IO code demonstrates this clearly.
Stephen, I see one big difference between ll_rw_block and the proposed tcp_sendpage():
You must allocate and initialize a complete buffer head for each page you want to read, and then you pass the array of buffer heads to ll_rw_block with one function call.
I'm certain the overhead is the allocation/initialization/freeing of the buffer heads, not the function call.
AFAICS the proposed tcp_sendpage interface is the other way around:
you need one function call for each page, but no memory allocation/setup. The memory is allocated internally by the tcp_sendpage implementation, and it merges requests when possible, thus for a 9000 byte jumbopacket you'd need 3 function calls to tcp_sendpage(MSG_MORE), but only one skb is allocated and set up.
Ingo is that correct?
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Manfred
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