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Re: [Qemu-devel] xen_disk qdevification (was: [PATCH 0/3] Performance im


From: Kevin Wolf
Subject: Re: [Qemu-devel] xen_disk qdevification (was: [PATCH 0/3] Performance improvements for xen_disk v2)
Date: Fri, 2 Nov 2018 13:14:30 +0100
User-agent: Mutt/1.10.1 (2018-07-13)

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

Thanks a lot, Paul! This is good news.

Kevin



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