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Re: [Xen-devel] More network tests with xenoprofile this time

To: William Cohen <wcohen@xxxxxxxxxx>, "Santos, Jose Renato G" <joserenato.santos@xxxxxx>
Subject: Re: [Xen-devel] More network tests with xenoprofile this time
From: Andrew Theurer <habanero@xxxxxxxxxx>
Date: Wed, 8 Jun 2005 14:20:02 -0500
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, Aravind Menon <aravind.menon@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, G John Janakiraman <john@xxxxxxxxxxxxxxxxxxx>, "Turner, Yoshio" <yoshio_turner@xxxxxx>
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> Hi Renato,
> The article was an interesting application of the xenoprof.
> It seem like it would be useful to also have data collected using the
> cycle counts (GLOBAL_POWER_EVENTS on P4) to give some indication of
> areas with high overhead operations. There may be some areas with few
> very expensive instructions. Calling attention to those areas would
> help improve performance.
> The increases in I-TLB and D-TLB events for Xen-domain0 shown in
> Figure 4 are surprising. Why would the working sets be that much
> larger for Xen-domain0 than regular linux, particularly for code? Is
> there an table similar to table 3 for I-TLB event sample locations?
> Can't the VMM use a 4-MB page and the Xen-domain0 kernel shouldn't be
> that much larger than regular linux kernel?  How were TLB flushes
> ruled out as a cause? Could the PERFCOUNTER_CPU counters in
> perfc_defn.h be used to see if the VMM is doing a lot of TLB flushes?

I had the same concern as you, and IMO, it seemed unlikely that the 
working set for dom0 would be so much larger to cause significant 
amount of TLB miss.  I also suspect TLB flushes to be the problem, but 
I have not had a chance to look at it.  I hope to very soon.


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