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

[Andrew Theurer <habanero@xxxxxxxxxx>]

> 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.

-Andrew

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