Re: [Xen-devel] [Qemu-devel] xen_disk qdevification

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Markus Armbruster [mailto:armbru@xxxxxxxxxx]
> Sent: 05 November 2018 15:58
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: 'Kevin Wolf' <kwolf@xxxxxxxxxx>; Tim Smith <tim.smith@xxxxxxxxxx>;
> Stefano Stabellini <sstabellini@xxxxxxxxxx>; qemu-block@xxxxxxxxxx; qemu-
> devel@xxxxxxxxxx; Max Reitz <mreitz@xxxxxxxxxx>; Anthony Perard
> <anthony.perard@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Qemu-devel] xen_disk qdevification
> 
> Paul Durrant <Paul.Durrant@xxxxxxxxxx> writes:
> 
> >> -----Original Message-----
> >> From: Kevin Wolf [mailto:kwolf@xxxxxxxxxx]
> >> Sent: 02 November 2018 11:04
> >> To: Tim Smith <tim.smith@xxxxxxxxxx>
> >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx; qemu-
> >> block@xxxxxxxxxx; Anthony Perard <anthony.perard@xxxxxxxxxx>; Paul
> Durrant
> >> <Paul.Durrant@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> >> Max Reitz <mreitz@xxxxxxxxxx>; armbru@xxxxxxxxxx
> >> 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.
> 
> Awesome!  Please coordinate with Anthony Prerard to avoid duplicating
> work if you haven't done so already.

Sure. I have already spoken to Anthony.

  Thanks,

   Paul


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