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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Feb 09, 2018 at 12:35:13PM +0100, Marek Marczykowski-Górecki wrote:
> 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.
> 

Sorry for the late reply.

If you really don't want block scripts, can you not specify a script
that only does "exit 0"? That seems to be easier than modifying libxl
and it is also useable in older versions of Xen.

Wei.

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