Re: XEN 4.11 and 9.99.48 DOMU performance

[Greg Troxel <gdt%lexort.com@localhost>]

Frank Kardel <kardel%netbsd.org@localhost> writes:

>> Have you done dd bs=1m from the dom0 raw disk, the dom0 backing file,
>> and the domU ('raw disk')?   I used to see X, 0.9X, and (0.9)^2 X, ish,
>> on somewhat old Xen and older NetBSD.
> Before this load test I reach 990Mb/s in DOMU instead of 1100Mb/s on DOM0.

That sounds good and slightly better than my 0.9^2, but close.

>> I also wonder if there is some sort of fsync in the domU leading to
>> virtual FUA leading to fsync in the dom0 going on.
>
> Could be, but in that case I would still expect a reasonably data
> stream to the disks then and not several seconds of inactivity.

Overall this smells like a locking bug.   You might try LOCKDEBUG in the
dom0.  You might also try 1 vcpu in the domU.