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: [Xen-users] About profiling xen

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [Xen-users] About profiling xen
From: Marco Tizzoni <marco.tizzoni@xxxxxxxxx>
Date: Thu, 1 Oct 2009 23:05:36 +0200
Cc: "Fajar A." <fajar@xxxxxxxxx>, Fasiha Ashraf <feehapk@xxxxxxxxxxx>, xen <xen-devel@xxxxxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Delivery-date: Thu, 01 Oct 2009 14:06:37 -0700
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:from:date:x-google-sender-auth:message-id:subject:to:cc :content-type:content-transfer-encoding; bh=HnvjZzMRedDMbD/5Vfx/Wifd81c/Sf9G3mFjLu+EFyo=; b=IsFwbvOsUAPa2vhfzGINTzm6FsqxvFgXWyCVTp/C7+7qDXkBuYxzNka0yNFgSjG2x9 ULbR7kePc5nXHQSiXOeXdgbhVdiik+mHqvAnrHXQJw1GYO8kPNoSsE6fgYAulf3EXqWJ cBeHL2NclQqzhOMBT7+gpfVeyQGwtifAGcwCk=
Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=jaMHHIb7RZ8TJkQw9g0f2l7nSPiMDmq4W3lYcXtR7BXNeL3vrsSTqVDjxZsfe5oOpA 6ydO5ww4CmlcgkKP/NUOOMuRnrQWrdg4KQ2xnm9x+8TVjWmar3kkbMOZ8j+OBcDz8su1 Kdx3CzeW/bgHwbMgrlGi2/cL7pbZ/0An0WZSE=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4AC516EC.3050704@xxxxxxxx>
List-help: <mailto:xen-users-request@lists.xensource.com?subject=help>
List-id: Xen user discussion <xen-users.lists.xensource.com>
List-post: <mailto:xen-users@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=unsubscribe>
References: <196324.1267.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <f9611b0f0909292333r7da0c616rbe53ca73a6ea512d@xxxxxxxxxxxxxx> <20090930063747.GG1434@xxxxxxxxxxx> <f9611b0f0909292340o6a53326aobcd87334d7cfaa6b@xxxxxxxxxxxxxx> <f9611b0f0909300045o55e22378xea270e9873471f1d@xxxxxxxxxxxxxx> <f9611b0f0909300206v53577d1cw300ff6092b8ffede@xxxxxxxxxxxxxx> <4AC3E889.6060407@xxxxxxxx> <f9611b0f0910010035m40949fb3o5efe60469b4466b7@xxxxxxxxxxxxxx> <4AC516EC.3050704@xxxxxxxx>
Sender: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
On Thu, Oct 1, 2009 at 10:54 PM, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> On 10/01/09 00:35, Marco Tizzoni wrote:
>> On Thu, Oct 1, 2009 at 1:23 AM, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
>>> Your clocksource is "xen", which is the best possible for a PV xen guest.
>>> However, a clocksource is for measuring elapsed time, not triggering
>>> timers.
>> Why? How would you solve the problem of raising events at a fixed rate?
> I'm not sure I follow you.  In the kernel, the clock*source* subsystem
> is for measuring time: its used to implement gettimeofday, as well as
> internal time accounting.  It isn't directly related to time events.


> The clock*event* mechanism is all about setting up timers to raise events.
> When running paravirtualized, we use Xen-specific versions of both.

Ok.  My problem is granularity. In xen I can't raise events more
frequently than 1000/s (with timer set to 1000hz).
Net test softwares such as netperf or hping use setitimer to send
packet at a fixed rate. On a non-xen box they works fine even  with
100k packets/sec (i.e. 100k alarms/sec). This can be problematic for
streaming software and more in general for soft real-time

>>> Unfortunately there doesn't seem to be a /sys file to show the
>>> current clockevent source in use, but if you have "xen" clocksource it's
>>> almost certainly the xen clockevent.
>>> However, this is only relevent if you have CONFIG_NO_HZ and
>> I've tried both set/unset but nothing change.
> Hm.  Its best to leave both enabled either way.
> Try the attached program to get some info about how well timers are
> working.  Compile with:

Thanks for your test, I tried and timers work as expected.


Xen-users mailing list