Re: support for sata7 Streaming Feature Set?

[Tejun Heo <htejun@gmail.com>]

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.

-- 
tejun