Messages in this thread | | | Date | Sun, 22 Jun 2008 10:35:41 -0400 (EDT) | From | Alan Stern <> | Subject | Re: Scatter-gather list constraints |
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On Sun, 22 Jun 2008, Andi Kleen wrote:
> > >> - Is it performance critical? > > > > For people using wireless USB drives, yes. > > But only if there is a lot of 512 byte block IO? The only case I can think > of right now would be XFS log IO and perhaps some O_DIRECT/raw device > accesses.
Sorry, I misunderstood your question. There probably will not be a lot of 512-byte block I/O -- not in the workloads I'm acquainted with. But there will be some.
It isn't performance-critical, in the sense that slowing down the odd 512-byte block transfers won't hurt performance much. But it is critical in the sense that the transfers must work properly when they do occur.
> If it's only an relative oddball just copying is fine imho.
You mean, have the USB stack allocate bounce buffers and copy the data between the S-G buffers (which may be in high memory) and the bounce buffers? We're talking about a potentially fairly large amount of data, say up to 100 KB. Is that really easier than splitting up an I/O request?
Alan Stern
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