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

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

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?

> 
> 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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