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Re: [Xen-users] Massive performance regression

  • To: Xen-users <Xen-users@xxxxxxxxxxxxx>
  • From: Phil Susi <psusi@xxxxxxxxxx>
  • Date: Wed, 28 Feb 2018 12:26:11 -0500
  • Delivery-date: Wed, 28 Feb 2018 17:26:49 +0000
  • List-id: Xen user discussion <xen-users.lists.xenproject.org>

On 2/28/2018 11:52 AM, Phil Susi wrote:
> On 2/28/2018 11:14 AM, Phil Susi wrote:
>> My server is running Ubuntu 16.04 using Xen 4.6.5-0ubuntu1.4.  There
>> must have been an update in the last few weeks that seems to have caused
>> a terrible performance regression.  When I try to fire up a testing vm
>> to test a live cd, it takes several minutes before anything shows up on
>> the display, and during that time, qemu-system-i386 is burning through
>> 100% of a cpu ( out of 8 ).

I found it.  I first tried reverting to an older Dom0 kernel without the
spectre patches to no avail.  Then I noticed that qemu had been patched
for it as well.  After reverting qemu, boot time for a livecd in a domU
went from 4.5 minutes ( where you never even see the LILO menu at all
and the guest kernel keeps reporting cpu soft lockups ) to less than 30

Whatever they did to qemu fscked it up.

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