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Re: [Xen-devel] libxl - avoid calling block script

On Fri, Feb 09, 2018 at 11:03:55AM +0000, Roger Pau Monné wrote:
> Really adding Ian and Wei.
> On Fri, Feb 09, 2018 at 10:55:24AM +0000, Roger Pau Monné wrote:
> > So the problem is creation time for domains that have quite a lot of
> > disks attached. Adding Ian and Wei who know more about the async
> > dispatch system, but I think (at least from a technical PoV) it
> > should be possible to parallelize device attachment and thus hotplug
> > script execution. Devices are independent from each other.

In theory yes, but in practice block script (at least on Linux) takes a
lock and serialize execution...

> > Also the Linux hotplug scripts in general seem extremely convoluted,
> > I'm not sure whether we could gain some speed there just by
> > simplification.

Well, we're comparing a bunch of fork+exec(), including starting bash
(default /bin/sh on most systems), with just a single stat() call...
Handling scripts in libxl itself also takes some time (in my case libxl
live in libvirt, which may or may not have an impact). For a domU with
4 disks, getting rid of hotplug scripts saved about 2s of startup time.

Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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