[libvirt] [virt-devel] Cache and memory bandwidth graphs: native versus guest

[john cooper]

Bill Gray wrote:
> 
> See attachment with two graphs: (1) cache bandwidth, (2) blowup of
> sustained memory bandwidth region...

Bill,
    I had some difficulty with this document under ooffice.
A recent version seized and an older version didn't seem
to render correctly.  Could you export it as pdf?

Thanks,

-john


> - X axis has a log scale
> 
> - Light blue line is an older system with 32K L1 and 6M L2 caches
> 
> - All other measurements on perf34: 32K L1, 256K L2, 30M L3 caches
> 
> - Majority of variation in L1 cache region is from the two guest
> measurements done with no taskset to a VCPU: yellow and maroon lines.
> Perhaps this reflects the test bouncing between VCPUs in the guest.
> 
> - The sustained memory bandwidth for the guest with no pinning is only
> 80% of native (maroon line), which motivates more convenient and
> comprehensive numactl for guests.
> 
> - Virtualized bandwidth is otherwise nearly in line with native, which
> confirms the importance of the virtual CPUID communicating actual native
> cache sizes to cache-size-aware guest applications, since guest apps
> could benefit from the full size of the native cache.  (Guest was
> started with "-cpu host", but lscpu in guest showed 4M cache despite
> actual 30M cache.)


-- 
john.cooper at redhat.com