On 08/12/2012 05:37 AM, Michael S. Tsirkin wrote:
AFAIK Xin left Intel and is not working on it.
Contributions are welcome.
That's too bad... do you know of anyone else (at Intel or otherwise) who
might be familiar enough with the existing codebase to get me started?
From the code I've looked at, it appears that among other things
they're using the splice(2) / vmsplice(2) system calls to effect
"copying" without actually copying data. If I understand the semantics
correctly, these calls are basically shuffling pointers around to avoid
unnecessary memcpy(3) / mmap(2) calls. I've even seen a "zero-copy"
version of sendfile(2) that essentially wraps it around a call to splice(2).
I may be able to hack something together based on the current zero-copy
TX implementation, but as I'm still wrapping my head around several of
the concepts I just described, it may be awhile before I can produce
anything useful. I have quite a bit of experience developing for Linux
in C, but this would be my first attempt at writing kernel/device-driver
code.
The Release Notes for RHEL 6.2 (originally published on 12/06/2011)
also specifically mention macvtap/vhost zero-copy capabilities as
being included as a Technology Preview:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/6.2_Release_Notes/virtualization.html
I think this means TX.
It does. I meant to clarify that point in my original email... yes, only
TX zero-copy is currently implemented, and it is still marked as
"experimental". Outside of the custom solutions like PF_RING that I
mentioned, I don't know that I've seen zero-copy for RX.
-- Robert Vineyard
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