[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] Re: Poor performance on HVM (kernbench)

  • To: "Gianluca Guida" <gianluca.guida@xxxxxxxxxxxxx>
  • From: "Todd Deshane" <deshantm@xxxxxxxxx>
  • Date: Thu, 11 Sep 2008 15:04:03 -0400
  • Cc: Muli Ben-Yehuda <MULI@xxxxxxxxxx>, George Dunlap <dunlapg@xxxxxxxxx>, xen-devel mailing list <xen-devel@xxxxxxxxxxxxxxxxxxx>, Anthony Liguori <aliguori@xxxxxxxxxx>
  • Delivery-date: Thu, 11 Sep 2008 12:04:25 -0700
  • Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:reply-to:to:subject:cc:in-reply-to :mime-version:content-type:content-transfer-encoding :content-disposition:references; b=UAN/NW7pVKj6Xifa0oi/D4tLOYs1VheJ60OpyG3mk6F2V7mG9JZmS8dePhSEy1o9jQ 11H4UDyswxUuz1NlYfULTqozYbaI7FdzzLV2kPHPs9pHuTuUhaKbGBgWCkNriUq8XleO O6dwI07OjB0XXX3UmKPrePYW1rbTIjMaZwPlc=
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

On Thu, Sep 11, 2008 at 2:26 PM, Gianluca Guida
<gianluca.guida@xxxxxxxxxxxxx> wrote:
> George Dunlap wrote:
>> So, the problem appears to be with a ton of brute-force searches to
>> remove writable mappings, both during resync and promotion.  My
>> analysis tool is reporting that of the 30 seconds or so in the trace
>> from xen-unstable, the guest spent a whopping 67% in the hypervisor:
>>  * 26% doing resyncs as a result of marking another page out-of-sync
>>  * 9% promoting pages
>>  * 27% resyncing as a result of cr3 switches
>> And almost the entirety of all of those can be attributed to
>> brute-force searches to remove writable mappings.
> Fantastic (well, sort of)!
> If I understand it correctly, Todd is using PV drivers in Linux HVM guests,
> so the reason for brute-force search is due to former L1 page-tables being
> used as I/O pages, not being unshadowed because they can get writable
> mappings out of it.
> It is, shortly, an unshadowing problem. Should be `easy` to fix. I wasn't
> using PV drivers, so I was not experiencing this behaviour.
> Or, it could be a fixup table bug, but I doubt it.
> George, did you saw excessive fixup faults in the trace?
> Todd, could you try without PV drivers (plain qemu emulation) and see if the
> results get better?

To the best of my knowledge, I am not using PV on HVM drivers since
they are not upstream.
I am using 2.6.27-rc4 xen domU kernel, with the normal xen PV drivers
and KVM virtio built in.
Am I mistaken?

I am running the test with shadow3 disabled now.
I'll report the results when they come out.

Any other suggestions or things for me to try, let me know.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.