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Re: [Xen-devel] Re: [Xen-users] About profiling xen

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [Xen-users] About profiling xen
From: Marco Tizzoni <marco.tizzoni@xxxxxxxxx>
Date: Wed, 30 Sep 2009 18:38:26 +0200
Cc: xen <xen-devel@xxxxxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
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On Wed, Sep 30, 2009 at 6:04 PM, Dan Magenheimer
<dan.magenheimer@xxxxxxxxxx> wrote:
>> How can I get a different, and I hope better, clocksource? In time.c I
>> found acpi and hpet are available.
> I'm no networking expert, but if your packets are
> only being processed once per HZ, that seems like
> a completely different problem.  Even if you are
> able to get a hardware high resolution timer, the
> resolution has nothing to do with the clock
> interrupt frequency (HZ).

Netperf use setitimer() to send packets at regular intervals to test
network speed.
If the timer is not finer enough the signal is not delivered on time
and becomes impossibile to reach the requested rate, i.e. if timer is
250Hz you can get at most 250 alarm/s.

>From my point of view this issue should be documented and as well as
the clocksource option. I cactched some information googling but it's
not clearly explained.


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