Wei Liu writes ("Re: [PATCH RFC 07/20] migration: defer precopy policy to
libxl"):
> On Thu, Mar 30, 2017 at 01:19:41AM -0400, Joshua Otto wrote:
> > Is the memcpy() really significant here? If this were a tight
> > loop, sure, but every invocation of the policy callback implies
> > both a 4MB network transfer _and_ a synchronous RPC.
>
> Ian, How can Joshua pass a pointer across RPC boundary to avoid excessive
> copying?
You can't pass a pointer across the IPC boundary. The two bits of
code run in different processes, with different address spaces.
Also, this precopy stats struct is tiny: two unsigned and a long.
Josuha is entirely right to ask whether the overhead is significant.
I think it isn't.
If the performance of the proposed arrangements is inadequate, the
whole design needs reconsideration - the synchronous callback is more
of a concer, as Joshua suggests. But I assume it's not, or Joshua
would have noticed !
Thanks,
Ian.
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