Re: [Xen-devel] [PATCH v10 4/5] remus: implement remus network buffering for nic devices

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Jackson writes ("Re: [PATCH v10 4/5] remus: implement remus network 
buffering for nic devices"):
> Shriram Rajagopalan writes ("Re: [PATCH v10 4/5] remus: implement remus 
> network buffering for nic devices"):
> ...
> > The async execution for each netlink call is an overkill.  These
> > rtnl calls complete in a matter of few microseconds utmost. On the
> > other hand, this code structure, fork/execs a new process for every
> > checkpoint just to execute a single library call (netbuf_epoch_op),
> > which in turn issues just a syscall.
> 
> I haven't read the code to check whether this criticism is accurate,
> but if it is I think it would be justified.
> 
> There is no need to use the async machinery for fast system calls.

Having read Shriram's other mail, I feel the need to emphasise the
qualification "fast".

"Fast" means "cannot ever, even in error conditions, take a
significant amount of time".  In particular anything that waits for
incoming network traffic is not "fast".

But AFAICT by looking at the code we are talking only about these
calls:
  rtnl_qdisc_plug_buffer
  rtnl_qdisc_plug_release_one
  rtnl_qdisc_add
Surely these always complete immediately.

Ian.

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