Re: [MirageOS-devel] Domain creation/boot times and Xen toolstack

[Magnus Skjegstad <magnus.skjegstad@xxxxxxxxxxxx>]

On Mon, 15 Dec 2014, at 11:56, Anil Madhavapeddy wrote:
> On 15 Dec 2014, at 03:10, Martin Lucina <martin@xxxxxxxxxx> wrote:
> > 
> > Hi Anil,
> > 
> > anil@xxxxxxxxxx said:
> >> There were a sequence of slow bits in xl that we progressively fixed.
> >> Most of these should be winding their way upstream as they get cleaned up.
> >> Improvements came from:
> >> 
> >> 1) Replace hotplug script with minimal version (currently a shell script)
> >> 2) Replace hotplug script with inline ioctl() gave even better results 
> >>   as no forking happened at all.
> >> 3) Parallelise hotplug with domain build.
> >> 4) Don't block on primary console
> >> 5) Use Dave's XenStore+Irmin with reduced transaction conflicts.
> >> 
> >> Number 3) is fairly invasive to libxl, and the XenstoreNG is still being
> >> prepared for release, but the minimal ioctl is pretty easy and could be the
> >> default.
> > 
> > Right, 1) and 2) matches what we found with Ian J. while quickly looking at
> > low-hanging fruit to optimize at the hack day after the conference.
> > 
> > Is there a version of xen.git with these patches that I can build and use
> > to test? I'd like to try spinning up large numbers of rump kernel based
> > domUs which is impractical with current domain creation times.
> 
> I'm travelling at the moment, but I can dig out the C file I wrote for
> the 2) case when I'm back next weekend.  Jon, Dave, do you have the
> working
> tree for your XL patches available anywhere?

This should be the C code we used for 2):
https://github.com/MagnusS/jitsu/blob/master/add_vif.c

> 
> > 
> > One thing not on your list is qemu spinup time; I presume this is because
> > you are not using blkfront? The default backend for blkfront is qtap which
> > unfortunately relies on qemu; vanilla Linux dom0 kernels don't appear to
> > support any other backends (eg. blktap).
> > 
> 
> We do use blkfront, but not the qemu blkback (which I've never understood
> to be honest -- why introduce qemu into the driver equation unless it's
> absolutely necessary?).  Xen-arm-builder has the blktap patches:
> https://github.com/mirage/xen-arm-builder/blob/master/patches/linux-0001-blktap2-fixups.xs.patch
> 
> Anil
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Magnus

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