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

To: "Santos, Jose Renato G" <joserenato.santos@xxxxxx>
Subject: Re: [Xen-devel] More network tests with xenoprofile this time
From: William Cohen <wcohen@xxxxxxxxxx>
Date: Tue, 07 Jun 2005 17:47:22 -0400
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, "Turner, Yoshio" <yoshio_turner@xxxxxx>, Andrew Theurer <habanero@xxxxxxxxxx>, Aravind Menon <aravind.menon@xxxxxxx>, G John Janakiraman <john@xxxxxxxxxxxxxxxxxxx>
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Santos, Jose Renato G wrote:

  You may want to take a look at the folowing paper
  which is being presented at VEE'05 (June 11 and 12, 2005).


  It presents network performance results using xenoprof.
  This was done for xen 2.0.3. The profile you reported
  has some similarities with our results although the
  exact numbers are different. But that is expected, since
  you are running a different version of Xen on a different
hardware. We have seen that a significant amount of time was spent on handling interrupts in Xen, as well. We have also seen that a significant amount of time is spent on the hypervisor (+/- 40%) for the dom1 <-> external
  case, measured both at dom1 and at dom0.
  (in our case we instrumented the receive side)
  When we run the benchmark on dom0 the time spent on Xen
is reduced to (+/-20%). Most of this extra Xen overhead when running a guest
  seems to come from the page transfer between
  domain 0 and the guest (see table 6 and discussion
  on paper).
The paper omits the complete oprofile reports
  for brevity. I will be happy to send you any
  detailed oprofile report we have generated for the
paper, if you want to compare it with your results. Just let me know ...


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?

Also how much of I-TLB and D-TLB events are due to the P4 architecture? Are the results so dramatic for a Athlon or AMD64 processors?


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