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

[Kevin Wolf <kwolf@xxxxxxxxxx>]

Am 02.11.2018 um 12:13 hat Paul Durrant geschrieben:
> > -----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.

Thanks a lot, Paul! This is good news.

Kevin

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