Re: memory performance 20% degradation in DomU -- Sisu

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Mar 04, 2014 at 05:00:46PM -0600, Sisu Xi wrote:
> Hi, all:
> 
> I also used the ramspeed to measure memory throughput.
> http://alasir.com/software/ramspeed/
> 
> I am using the v2.6, single core version. The command I used is ./ramspeed
> -b 3 (for int) and ./ramspeed -b 6 (for float).
> The benchmark measures four operations: add, copy, scale, and triad. And
> also gives an average number for all four operations.
> 
> The results in DomU shows around 20% performance degradation compared to
> non-virt results.

What kind of domU? PV or HVM?
> 
> Attached is the results. The left part are results for int, while the right
> part is the results for float. The Y axis is the measured throughput. Each
> box contains 100 experiment repeats.
> The black boxes are the results in non-virtualized environment, while the
> blue ones are the results I got in DomU.
> 
> The Xen version I am using is 4.3.0, 64bit.
> 
> Thanks very much!
> 
> Sisu
> 
> 
> 
> On Tue, Mar 4, 2014 at 4:49 PM, Sisu Xi <xisisu@gmail.com> wrote:
> 
> > Hi, all:
> >
> > I am trying to study the cache/memory performance under Xen, and has
> > encountered some problems.
> >
> > My machine is has an Intel Core i7 X980 processor with 6 physical cores. I
> > disabled hyper-threading, frequency scaling, so it should be running at
> > constant speed.
> > Dom0 was boot with 1 VCPU pinned to 1 core, with 2 GB of memory.
> >
> > After that, I boot up DomU with 1 VCPU pinned to a separate core, with 1
> > GB of memory. The credit scheduler is used, and no cap is set for them. So
> > DomU should be able to access all resources.
> >
> > Each physical core has a 32KB dedicated L1 cache, 256KB dedicated L2
> > cache. And all cores share a 12MB L3 cache.
> >
> > I created a simple program to create an array of specified size. Load them
> > once, and then randomly access every cache line once. (1 cache line is 64B
> > on my machine).
> > rdtsc is used to record the duration for the random access.
> >
> > I tried different data sizes, with 1000 repeat for each data sizes.
> > Attached is the boxplot for average access time for one cache line.
> >
> > The x axis is the different Data Size, the y axis is the CPU cycle. The
> > three vertical lines at 32KB, 256KB, and 12MB represents the size
> > difference in L1, L2, and L3 cache on my machine.
> > *The black box are the results I got when I run it in non-virtualized,
> > while the blue box are the results I got in DomU.*
> >
> > For some reason, the results in DomU varies much more than the results in
> > non-virtualized environment.
> > I also repeated the same experiments in DomU with Run Level 1, the results
> > are the same.
> >
> > Can anyone give some suggestions about what might be the reason for this?
> >
> > Thanks very much!
> >
> > Sisu
> >
> > --
> > Sisu Xi, PhD Candidate
> >
> > http://www.cse.wustl.edu/~xis/
> > Department of Computer Science and Engineering
> > Campus Box 1045
> > Washington University in St. Louis
> > One Brookings Drive
> > St. Louis, MO 63130
> >
> 
> 
> 
> -- 
> Sisu Xi, PhD Candidate
> 
> http://www.cse.wustl.edu/~xis/
> Department of Computer Science and Engineering
> Campus Box 1045
> Washington University in St. Louis
> One Brookings Drive
> St. Louis, MO 63130


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