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RE: [Xen-devel] Xenoprof in an HVM domain

To: <steved@xxxxxxxxxx>
Subject: RE: [Xen-devel] Xenoprof in an HVM domain
From: "Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>
Date: Mon, 24 Apr 2006 15:02:41 +0800
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Thread-topic: [Xen-devel] Xenoprof in an HVM domain
Hi Steve,
As we know, xenoprof 2.0 is checked in xen-unstable for days. Now I'm writing a 
patch to add passive domain support (which exists in UP guest age) for smp 
guest. Using passive domain and my improvement in oprofile (I sent out before), 
we needn't change guest code and can tune hvm guest in a somewhat raw way -- PC 
samples from hv and guest kernel can be mapped to functions but all samples 
from application are only there as a whole. It's enough for tuning hvm 
performace for now. 
You are proposing to add active domain support for hvm, right? The apparent 
advantage is to tune hvm linux applications in future. It should be doable, 
like we've enabled vbd/vnif in hvm. And it needs more effort in hvm. 
Yes, Hypervcall, shared buffer and notification mechanism are all needed. For 
the last one, one of simple way is: 1) in hvm guest kernel, register for an 
unused IRQ line 2) in hv, inject that interrupt to hvm when needed. Or you can 
use a psydo PCI device in qemu to hold one irq number.


-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Steve Dobbelstein
Sent: 2006年4月21日 13:11
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Xenoprof in an HVM domain

I'm looking into getting Xenoprof to tun in an HVM domain, since we will
eventually need a profiler for HVM domains to track down areas of poor
performance.  (HVMs have poor performance? :) )  Being relatively new to
OProfile, Xenoprof, and Xen internals, I would appreciate any pointers,
tips, and comments on how to work the implementation.  I see three basic
areas of work.

1. Implement hypercalls in HVM domains.  This has been done by Steve
Ofsthun of Virtual Iron who contributed his patches to the xen-devel list
recently.  (Thanks, Steve.)

2. Implement the shared buffer that conveys profile events from the
hypervisor to the domain.  From my initial crawl through the Xenoprof code
(see for example linux-2.6-xen-sparse/arch/i386/oprofile/xenoprof.c) it
appears that its setup of the shared buffer via hypercalls and page table
updates should work in an HVM domain.  Correct me if I'm wrong.

3. Implement an interrupt mechanism for the hypervisor to signal the domain
that it has more data in the shared buffer.  Xenoprof currently sets up an
event channel for this.  In my initial hack of the code I discovered that
the event channel used by Xenoprof conflicts with the 8259 support in the
HVM kernel.  Since I use the serial interface to the HVM domain, I am
hesitant to remove the 8259 support in my HVM kernel.  It appears that I
need to either get an event channel to work through qemu, preserving the
8259 functionality, or change Xenoprof in the hypervisor to instruct qemu
to issue an interrupt to the domain and change Xenoprof in the domain to
run off an interrupt instead of an event channel.  Or maybe I don't know
what I'm talking about and need to be enlightened by those who know better
what the issues are.

Any advice is appreciated.

Steve D.

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