This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


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

To: "Gianluca Guida" <gianluca.guida@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: Poor performance on HVM (kernbench)
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
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:reply-to :to:subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references; bh=Jz7YOXet1rDZAFwF5jYImDCYb2vK4lEY3+9eb6Th1Pk=; b=ZMqkNY1RJts0UJZzAHesUmP3mnYDnJotqXLXi2gVSsh7PMtph6lC3faNfWqjw2exmN Yvs4GHjFpb7y1BwC4XrzSI6M96R6GcTqF4E8JaTMwgqtqGIDU5lLDzZgr/BuCWZ+m7IS 4QjZDml23WWLjniEgE2dL8mjbVA4szJb+pWNU=
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=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <48C962D8.5030102@xxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <1e16a9ed0809101123m71a12030v7d06501f6467f93@xxxxxxxxxxxxxx> <1e16a9ed0809101422p6a58304dxaa1a92847109a518@xxxxxxxxxxxxxx> <48C8EC48.6080507@xxxxxxxxxxxxx> <48C9367B.6090003@xxxxxxxxxxxxx> <1e16a9ed0809110835p73165150t3f78d75b2f2ca8eb@xxxxxxxxxxxxxx> <48C9548C.4060709@xxxxxxxxxxxxx> <de76405a0809111107r387487b5s7aa6d87d0401ce5@xxxxxxxxxxxxxx> <48C962D8.5030102@xxxxxxxxxxxxx>
Reply-to: deshantm@xxxxxxxxx
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
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

<Prev in Thread] Current Thread [Next in Thread>