New MPI benchmark performance results (update)

New MPI benchmark performance results (update)

[xuehai zhang]

Hi all,

In the following post I sent in early April 
(http://lists.xensource.com/archives/html/xen-devel/2005-04/msg00091.html), I reported some 
performance gap when running PMB SendRecv benchmark on both native Linux and domU. Now I've prepared 
a webpage comparing 8 PMB benchmarks' performance under 4 scenarios (native Linux, dom0, domU with 
SMP, and domU without SMP) at http://people.cs.uchicago.edu/~hai/vm1/vcluster/PMB/.

In the graphs presented on the webpage, we take the results of native Linux as the reference and 
normalize the other 3 scenarios to it. We observe a general pattern that usually dom0 has a better 
performance than domU with SMP than domU without SMP (here better performance means low latency and 
high throughput). However, we also notice very big performance gap between domU (w/o SMP) and native 
linux (or dom0 because generally dom0 has a very similar performance as native linux). Some distinct 
examples are: 8-node SendRecv latency (max domU/linux score ~ 18), 8-node Allgather latency (max 
domU/linux score ~ 17), and 8-node Alltoall latency (max domU/linux > 60). The performance 
difference in the last example is HUGE and we could not think about a reasonable explaination why 
transferring 512B message size is so much different than other sizes. We appreciate if you can 
provide your insight to such a big performance problem in these benchmarks.

BTW, all the benchmarking is based on the original Xen code. That is, we didn't modify the 
net_rx_action netback to kick the frontend after every packet as suggested by Ian in the following 
post (http://lists.xensource.com/archives/html/xen-devel/2005-04/msg00180.html)

Please let me know if you have any questions about the configuration of the benchmarking 
experiments. I am looking forward to your insightful explainations.

Thanks.

Xuehai

Re: New MPI benchmark performance results (update)

[Steven Hand]

> Please let me know if you have any questions about the configuration
> of the benchmarking experiments. I am looking forward to your
> insightful explainations.

Erm, what version of Xen are you using for these? I notice that the 
dom0 kernel seems to be using 2.4.28 which is not current in any of 
the trees. Since you're using SMP guests, I'm guessing this is some
old version of xen-unstable? 

Your results are kinda interesting but I think you'd probably be
better off trying to compare like with like so that we can isolate
the performance issues due to Xen/XenLinux, i.e. 

  - use the same kernel (or ported kernel) in each case; 
  - use the same amount of memory in each case. 

Otherwise you end up comparing 2.4 to 2.6, or 128MB/360MB/512MB, ...

Also you should probably use the current unstable tree since there
have been a number of performance fixes.


cheers,

S.

Re: New MPI benchmark performance results (update)

[xuehai zhang]

Steven,

Thanks for the response.

>>Please let me know if you have any questions about the configuration
>>of the benchmarking experiments. I am looking forward to your
>>insightful explainations.
> 
> 
> Erm, what version of Xen are you using for these? I notice that the 
> dom0 kernel seems to be using 2.4.28 which is not current in any of 
> the trees. Since you're using SMP guests, I'm guessing this is some
> old version of xen-unstable? 

The Xen version is 2.0 for all the experiments. I am not sure if the SMP mentioned in my email is 
the same as "SMP guests" you mentioned. To clarify, "domU with SMP" I mentioned means Xen is booted 
with SMP support (no "nosmp" option) and I pin dom0 to the 1st CPU and pin domU to the 2nd CPU; 
"domU with no SMP" I mentioned means Xen is booted without SMP support (with "nosmp" option) and 
both dom0 and domU use the same single CPU.

> Your results are kinda interesting but I think you'd probably be
> better off trying to compare like with like so that we can isolate
> the performance issues due to Xen/XenLinux, i.e. 

I agree with your suggestion.

>   - use the same kernel (or ported kernel) in each case; 

I will use 2.6 kernel for both dom0 and domU. For native linux, the current kernel version is 2.4 
and I have to convince the cluster administrator to upgrade it to 2.6 for a fair comparison as you 
point out.

>   - use the same amount of memory in each case. 

It is hard to use the same amount of memory, especially for domU memory because dom0 will occupy 
part of the 512MB physical memory. BTW, we think the memory is unlikely a key factor to the 
performance because the maximum message size is 4MB and we only test up to 8-node cluster (8 
processes) and the memory will not be overallocated.

> Otherwise you end up comparing 2.4 to 2.6, or 128MB/360MB/512MB, ...
> 
> Also you should probably use the current unstable tree since there
> have been a number of performance fixes.

I will grab the current unstable tree and rerun the experiments by integrating the above 
configuration improvements. I will send a new result update when I finish.

Thanks again for the help.

Xuehai

> cheers,
> 
> S.
> 
> 

Re: New MPI benchmark performance results (update)

[Mark Williamson]

> I will grab the current unstable tree and rerun the experiments by
> integrating the above configuration improvements. I will send a new result
> update when I finish.

Any bug fixes should also have gone into the -testing tree, which is part of 
the 2.0 series.

Cheers,
Mark

Re: New MPI benchmark performance results (update)

[xuehai zhang]

Mark Williamson wrote:
>>I will grab the current unstable tree and rerun the experiments by
>>integrating the above configuration improvements. I will send a new result
>>update when I finish.
> 
> 
> Any bug fixes should also have gone into the -testing tree, which is part of 
> the 2.0 series.

Mark,
Thanks for the reminding. I will try the -testing tree instead of -unstable tree then. BTW, could 
you please provide me some information about the current status of the Atropos scheduler? I sent out 
an email earlier to ask about it but no response so far. Thanks again.
Xuehai

Re: New MPI benchmark performance results (update)

[Nivedita Singhvi]

xuehai zhang wrote:
> Hi all,
> 
> In the following post I sent in early April 
> (http://lists.xensource.com/archives/html/xen-devel/2005-04/msg00091.html), 

Hi, thanks for sharing the data - it was interesting.
I tried to find additional data on the benchmarks using
the link you have for the user manual but it gave me
a 404 Error. It wasn't clear whether your benchmarks
use TCP or UDP or possibly raw sockets?

As has been pointed out by several people, running the
2.6 kernel and comparing apples to apples as much as possible
would help.

Is there any chance you kept some of the system statistics
and settings (netstat -s, sysctl -a info)?.
Did you tune the settings for the system at all?

> Alltoall latency (max domU/linux > 60). The performance difference in 
> the last example is HUGE and we could not think about a reasonable 
> explaination why transferring 512B message size is so much different 
> than other sizes. We appreciate if you can provide your insight to such 
> a big performance problem in these benchmarks.

You have an anomalous point on most of the results - and again,
knowing what kind of traffic this is would really help.

thanks,
Nivedita

Re: New MPI benchmark performance results (update)

[xuehai zhang]

Hi Nivedita,

Thanks for the response and the suggestion!

>> Hi all,
>>
>> In the following post I sent in early April 
>> (http://lists.xensource.com/archives/html/xen-devel/2005-04/msg00091.html), 
> 
> 
> 
> Hi, thanks for sharing the data - it was interesting.
> I tried to find additional data on the benchmarks using
> the link you have for the user manual but it gave me
> a 404 Error. 

I corrected the link error and now you can access the user manual through the link.

> It wasn't clear whether your benchmarks
> use TCP or UDP or possibly raw sockets?

I've read through the PMB user manual and it doesn't mention the communication protocol it uses. 
However, I do read "typically TCP/IP is the protocol used over Ethernet networks for MPI 
communications" from several references.

> As has been pointed out by several people, running the
> 2.6 kernel and comparing apples to apples as much as possible
> would help.

I fully agree with that and currently I try to rerun the experiments by using the same kernel 
versions for both dom0 and domU (maybe native linux too).
> 
> Is there any chance you kept some of the system statistics
> and settings (netstat -s, sysctl -a info)?.

I did not collect them while running the benchmarks, but I will try to log them when I rerun the 
experiments.

> Did you tune the settings for the system at all?
No, I did not do any specific things to tune the system.

>> Alltoall latency (max domU/linux > 60). The performance difference in 
>> the last example is HUGE and we could not think about a reasonable 
>> explaination why transferring 512B message size is so much different 
>> than other sizes. We appreciate if you can provide your insight to 
>> such a big performance problem in these benchmarks.
> 
> 
> You have an anomalous point on most of the results - and again,
> knowing what kind of traffic this is would really help.

I will try to dig into the source code and find it out.

Thanks again for the help.

Xuehai
> 
> thanks,
> Nivedita
> 
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 

RE: New MPI benchmark performance results (update)

[Ian Pratt]

> 
> In the graphs presented on the webpage, we take the results 
> of native Linux as the reference and normalize the other 3 
> scenarios to it. We observe a general pattern that usually 
> dom0 has a better performance than domU with SMP than domU 
> without SMP (here better performance means low latency and 
> high throughput). However, we also notice very big 
> performance gap between domU (w/o SMP) and native linux (or 
> dom0 because generally dom0 has a very similar performance as 
> native linux). Some distinct examples are: 8-node SendRecv 
> latency (max domU/linux score ~ 18), 8-node Allgather latency 
> (max domU/linux score ~ 17), and 8-node Alltoall latency (max 
> domU/linux > 60). The performance difference in the last 
> example is HUGE and we could not think about a reasonable 
> explaination why transferring 512B message size is so much 
> different than other sizes. We appreciate if you can provide 
> your insight to such a big performance problem in these benchmarks.

I still don't quite understand your experimental setup. What version of
Xen are you using? How many CPUs does each node have? How many domU's do
you run on a single node?

As regards the anomalous result for 512B AlltoAll performance, the best
way to track this down would be to use xen-oprofile. Is it reliably
repeatable? Really bad results are usually due to packets being dropped
somewhere -- there hasn't ben a whole lot of effort put into UDP
performance because so few applications use it.

Ian


 

Re: New MPI benchmark performance results (update)

[xuehai zhang]

Ian,

Thanks for the response.

>>In the graphs presented on the webpage, we take the results 
>>of native Linux as the reference and normalize the other 3 
>>scenarios to it. We observe a general pattern that usually 
>>dom0 has a better performance than domU with SMP than domU 
>>without SMP (here better performance means low latency and 
>>high throughput). However, we also notice very big 
>>performance gap between domU (w/o SMP) and native linux (or 
>>dom0 because generally dom0 has a very similar performance as 
>>native linux). Some distinct examples are: 8-node SendRecv 
>>latency (max domU/linux score ~ 18), 8-node Allgather latency 
>>(max domU/linux score ~ 17), and 8-node Alltoall latency (max 
>>domU/linux > 60). The performance difference in the last 
>>example is HUGE and we could not think about a reasonable 
>>explaination why transferring 512B message size is so much 
>>different than other sizes. We appreciate if you can provide 
>>your insight to such a big performance problem in these benchmarks.
> 
> 
> I still don't quite understand your experimental setup. What version of
> Xen are you using? How many CPUs does each node have? How many domU's do
> you run on a single node?

The Xen version is 2.0. Each node has 2 CPUs. "domU with SMP" I mentioned in the previous email 
means Xen is booted with SMP support (no "nosmp" option) and I pin dom0 to the 1st CPU and pin domU 
to the 2nd CPU; "domU with no SMP" I mentioned means Xen is booted without SMP support (with "nosmp" 
option) and both dom0 and domU use the same single CPU. There is only 1 domU running on a single 
node for each experiment.

> As regards the anomalous result for 512B AlltoAll performance, the best
> way to track this down would be to use xen-oprofile. 

I am not very familar with xen-oprofile. I notice there are some discussions about it in the mailing 
list. I wonder if there is any other documents that I can refer to. Thanks.

> Is it reliably repeatable? 

Yes, we observe this anomaly repeatable. The reported data point in the graph is the average of 10 
different runs of the same experiment in different time.

> Really bad results are usually due to packets being dropped
> somewhere -- there hasn't ben a whole lot of effort put into UDP
> performance because so few applications use it.

To clarify: do you indicate that benchmark like AlltoAll might use UDP rather than TCP as 
transportation protocol?

Thanks again for the help.

Xuehai

RE: New MPI benchmark performance results (update)

[Santos, Jose Renato G (Jose Renato Santos)]

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> I am not very familar with xen-oprofile. I notice there are 
> some discussions about it in the mailing 
> list. I wonder if there is any other documents that I can 
> refer to. Thanks.
> 

  Please, see http://xenoprof.sourceforge.net for a description
  of xenoprof and for downloading patches.(You will need 3 
  patches: one for xen, one for linux and one for oprofile). 
  You need to be familiar with oprofile to use xenoprof. Please check
  http://oprofile.sourceforge.net/ for more info on oprofile.

  Xenoprof is currently available only for Xen 2.0.5.
  I am working on getting it to xen unstable but there
  is a problem with NMI handling which was not solved yet.
   
  I have also attached a text file that gives an overview
  of xenoprof

  Renato

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                XENOPROF - Performance profiling in Xen
               =========================================

                           User Guide
                          ============

 Version: 1.0
 Date: April 8, 2005
 Copyright (C) 2005 Hewlett-Packard Co. (http://xenoprof.sourceforge.net)

 (Aravind Menon, Jose Renato Santos, Yoshio Turner, G.(John) Janakiraman)
 

1. Overview
===========

This file provides an overview of Xenoprof, a system-wide statistical 
profiling toolkit implemented for the Xen virtual machine environment.
The Xenoprof toolkit supports system-wide coordinated profiling in a 
Xen environment to obtain the distribution of hardware events such as 
clock cycles, instruction execution, TLB and cache misses, etc. Xenoprof 
allows profiling of concurrently executing virtual machines (which 
includes the operating system and applications running in each virtual 
machine) and the Xen VMM itself. Xenoprof provides profiling data at the 
fine granularity of individual processes and routines executing in either 
the virtual machine or in the Xen VMM

Xenoprof was developed at HP Labs by modifying and extending the 
original OProfile code for linux (http://oprofile.sourceforge.net).  
We assume the reader is familiar with OProfile and its tools. If you
are not familiar with OProfile we suggest that you read the OProfile
user manual at http://oprofile.sourceforge.net/docs before using Xenoprof.

System wide profiling in Xen requires the cooperation of 3 software
components at different levels of the software stack.

a) Xenoprof: 

   Extensions to the Xen hypervisor to support system-wide statistical
   profiling.  Xenoprof programs hardware performance counters to
   generate sampling interrupts at regular event count intervals, and
   handles the Non Maskable Interrupts (NMI) generated by the
   performance counters at overflow.  The NMI handler samples the
   program counter (PC) at the time of interrupt and stores the PC
   value in a per domain sample buffer.  Domains interact with
   Xenoprof using a specific hypercall.  This hypercall enables
   domains to define the hardware performance events to be sampled and
   their parameters (e.g., overflow interval), as well as to control
   the start and end of profiling.  Domains are notified of new PC
   samples in their respective sample buffers using the virtual
   interrupt mechanism provided by Xen (e.g., event notification).

b) OProfile kernel module:

   This module is responsible for interpreting the PC samples received
   from Xenoprof and mapping the PC sample to the appropriate routine
   in user, kernel or hypervisor level.  The original OProfile kernel
   module for linux was modified to use the Xenoprof interface instead
   of accessing the hardware counters directly.

   The OProfile module is organized in two main components: a low
   level driver, specific to a particular CPU model, and a generic
   module that is independent of the specific CPU model and implements
   the higher level profiling functions.  To enable OProfile to be
   used with Xenoprof, a new low level driver specific to Xen was
   created.  This driver accesses the hypervisor through the exposed
   Xenoprof interface, while the high level generic module was kept
   almost unmodified, except for minor changes necessary to interpret
   performance events associated with the hypervisor.

c) OProfile user level daemon and tools:

   The user level daemon is responsible for collecting the performance
   event samples from the kernel module and storing them on files for
   later processing and reporting.  The user level tools implement
   commands that enable the user to start and stop a profiling
   session, selecting the appropriate performance events and
   parameters as well as to generate reports.  In order to be used in
   a Xen environment these tools were slightly modified.  In
   particular, new command line options were added to the opcontrol
   command as described below.


2. Profiling multiple domains
=============================

A profiling session may profile one, a subset, or all domains running
in a particular physical machine.  In every profiling session one of
the domains takes the role of the initiator, which is responsible for
configuring, starting and stopping the session.  Other domains can be
included in the session as active participants or passive
participants.  Active participants are domains which have an active
OProfile kernel module that can map a PC sample to the appropriate
routine in user, kernel or hypervisor level, given that the CPU was
executing that domain when the PC was sampled.  Passive participants
do not need to be executing an OProfile kernel module.  For these
domains performance profiling is done at a coarser granularity with PC
samples being assigned to the domain as whole, instead of to specific
routines.  Passive domains are useful when profiling systems running
domains with operating systems that do not support the OProfile kernel
module or equivalent.  Note that the initiator must always be an
active domain.  The initiator will process the PC samples of all
passive domains.

A performance event (generated when one of the hardware performance
counters overflows) is delivered to the appropriate domain, depending
on the type of domain running at the time of the event.  If the
running domain is an active domain the PC sample is delivered to that
domain.  If the running domain is a passive domain, the PC sample is
delivered to the initiator.  If the running domain is not included in
the profiling session, the PC sample is discarded.


3) Extensions to OProfile user level commands
=============================================

A few command line options were added to OProfile command "opcontrol"
for use in Xen environments. The new command line options are:

a) --xen=<xen_image_file>
   This option is used to specify the xen image (e.g. xen-syms). This
   is used to resolve PC samples collected when executing the
   hypervisor.

b) --active-domains=<list> 
   (where <list> is a list of comma separated domain ids)

   This option is used in the initiator domain to specify the list of
   active domains to be profiled.  The specification of the initiator
   domain id in the list of active domains is not necessary.  The
   initiator domain will always be considered an active domain and its
   inclusion on the specified active domain list is optional.

   For example: --active-domains=2,5,6 indicates that domains 2, 5 and
   6 are active domains. Assuming that domain 0 was the initiator the
   previous specification would be equivalent to
   --active-domains=0,2,5,6.

c) --passive-domains=<list>
   This option is used to specify the list of passive domains.


Besides opcontrol no other OProfile commands were modified for use in
Xen environments.

Full system profiling reports can be easily obtained by concatenating
the individual reports of each active domain, using the regular
opreport command in each active domain.  New tools that combine
multiple reports on a single system-wide report can be implemented in
the future.

4) Multi-domain profiling
=========================

In order to start and stop a profiling session across multiple domains
a set of OProfile commands must be executed in the multiple domains in
a coordinated way.  A typical sequence of commands for starting and
stopping profiling are listed below

 A) Sequence of commands to start profiling:
     1) On the initiator domain
         > opcontrol --reset
           (clear out any previous data of current session)
         > opcontrol --start-daemon
                     [--active-domains=<active_list>]
                     [--passive-domains=<passive_list>] ...
           (start OProfile daemon and specify the set of active and
           passive domains in the session)

     2) On each active domain
         > opcontrol --reset
         > opcontrol --start
         (indicates domain is ready to process performance events)
     3) On initiator
         > opcontrol --start
         (Multi-domain profiling session starts)
         (This is only successful if all active domains are ready)

 B) Sequence of commands to stop profiling
     1) On each active domain
         > opcontrol --stop
     2) On initiator domain
         > opcontrol --stop

5) Current supported configurations 

  a) Xen versions:           Xen 2.0.3 to 2.0.5
  b) Processor architecture: X86
  c) Processor models:       Pentium 4, Pentium iii
  d) Active Domains:         Uniprocessor - linux 2.6. (No SMP, No linux 2.4)
  e) Passive Domains:        No restriction

6) Patch files
==============

  In order to run OProfile in Xen environments three patches are needed:
  a) xenoprof-1.0-xen-2.0.5.patch
     Patch for Xen hypervisor.
  b) xenoprof-1.0-linux-2.6.10.patch
     Patch for Linux 2.6.10 (Apply to linux-sparse tree in Xen source tree)
  c) xenoprof-1.0-oprofile-0.8.1.patch
     Patch for OProfile 0.8.1

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