Re: support for sata7 Streaming Feature Set?

From: Tejun Heo
Date: Thu May 18 2006 - 19:12:19 EST

Jeff Garzik wrote:
Tejun Heo wrote:
One thing to think about before supporting streaming from/to harddisks from userland is how to make data flow efficiently from userland to kernel and back. But, no matter what, kernel <-> userland usually involves one data copy, so I don't think making sg similarly efficient would be too difficult (it might be already).

Actually, the kernel usually maps userland pages, eliminating the need for a copy. write(2) may have copied data into that page originally, but mmap(2) need not have.

Yeap, to achieve high streaming rate, it would be best to have preallocated ring buffer and ring pointers. If this high-bw streaming thing becomes common, we can add it to sg, I guess.

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