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

[Markus Armbruster <armbru@xxxxxxxxxx>]

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.

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