Re: [Qemu-devel] xen_disk qdevification (was: [PATCH 0/3] Performance improvements for xen_disk v2)

[Paul Durrant]

> -----Original Message-----
> From: Kevin Wolf [mailto:address@hidden
> Sent: 02 November 2018 11:04
> To: Tim Smith <address@hidden>
> Cc: address@hidden; address@hidden; qemu-
> address@hidden; Anthony Perard <address@hidden>; Paul Durrant
> <address@hidden>; Stefano Stabellini <address@hidden>;
> Max Reitz <address@hidden>; address@hidden
> Subject: xen_disk qdevification (was: [PATCH 0/3] Performance improvements
> for xen_disk v2)
> 
> Am 02.11.2018 um 11:00 hat Tim Smith geschrieben:
> > A series of performance improvements for disks using the Xen PV ring.
> >
> > These have had fairly extensive testing.
> >
> > The batching and latency improvements together boost the throughput
> > of small reads and writes by two to six percent (measured using fio
> > in the guest)
> >
> > Avoiding repeated calls to posix_memalign() reduced the dirty heap
> > from 25MB to 5MB in the case of a single datapath process while also
> > improving performance.
> >
> > v2 removes some checkpatch complaints and fixes the CCs
> 
> Completely unrelated, but since you're the first person touching
> xen_disk in a while, you're my victim:
> 
> At KVM Forum we discussed sending a patch to deprecate xen_disk because
> after all those years, it still hasn't been converted to qdev. Markus is
> currently fixing some other not yet qdevified block device, but after
> that xen_disk will be the only one left.
> 
> A while ago, a downstream patch review found out that there are some QMP
> commands that would immediately crash if a xen_disk device were present
> because of the lacking qdevification. This is not the code quality
> standard I envision for QEMU. It's time for non-qdev devices to go.
> 
> So if you guys are still interested in the device, could someone please
> finally look into converting it?
> 

I have a patch series to do exactly this. It's somewhat involved as I need to 
convert the whole PV backend infrastructure. I will try to rebase and clean up 
my series a.s.a.p.

  Paul

> Kevin